Technical Manual Lsc Alternators

1

TECHNICAL MANUAL

LSC ALTERNATORS

INDEX

Description Page

SECTION 1 GENERAL

1.1 Intended Use-------------------------------------------------- 7

1.2 Type-------------------------------------------------------------- 7

1.3 Product Range----------------------------------------------- 7

1.4 Standards------------------------------------------------------ 8

1.5 Power Ratings ------------------------------------------------ 8

1.5.1 Duty “S1” operation: Continuous------------- 8

1.5.2 Duty “SCH” operation: Worksite--------------- 8

1.5.3 Duty “SEC” operation: Standby---------------- 8

1.6 Voltage & Frequency ------------------------------------- 9

1.7 Speed------------------------------------------------------------ 9

1.8 Frequency------------------------------------------------------ 9

SECTION 2 ‘LSC’ Alternators features

2.1 Quality----------------------------------------------------------- 11

2.2 Salient Mechanical Features---------------------------- 11

2.2.1 Stator Frame ----------------------------------------- 11

2.2.2 Rotor Core -------------------------------------------- 11

2.2.3 Dynamic Balancing-------------------------------- 11

2.2.4 Terminal Box------------------------------------------- 11

2.2.5 Bearings------------------------------------------------ 11

2.2.6 Cooling------------------------------------------------- 12

2.2.7 Tropicalisation---------------------------------------- 12

2.2.8 Enclosure----------------------------------------------- 13

2.2.9 Mounting----------------------------------------------- 14

2.3 Salient Electrical Features-------------------------------- 15

2.3.1 Power Factor----------------------------------------- 15

2.3.2 Insulation Class--------------------------------------- 15

2.3.3 Excitation system------------------------------------ 16

2.3.3.1 Principle of operation--------------------------- 16

2

INDEX

Description Page 2.3.3.2 Shunt Field Excitation --------------------------- 16

2.3.3.3 AREP Excitation system------------------------- 17

2.3.3.4 PMI Feature----------------------------------------- 18

2.4 AREP Winding & Short circuit withstand capability ------------------------------------------------------

18

2.5 Voltage adjustment range------------------------------ 18

2.6 Voltage Regulation----------------------------------------- 18

2.7 Voltage wave form----------------------------------------- 19

2.8 Transient Voltage dip ------------------------------------- 19

2.9 Radio Interference------------------------------------------ 20

2.10 Over load capacity of ‘LSC’ alternators------------ 20

2.11 Automatic Voltage Regulator-------------------------- 21

2.11.1 Types of AVRs--------------------------------------- 21

2.11.2 Technical Data------------------------------------- 22

2.11.3 Special Features of AVR R448----------------- 23

2.11.4 Special Features of AVR R449----------------- 23

2.11.5 Under Frequency Roll off----------------------- 24

2.11.6 Diode Failure Monitor---------------------------- 24

SECTION 3 Sizing of alternators

3.1 Standard Specification Rating Chart---------------- 26

3.2 Effect of different loads on alternator kVA rating-------------------------------------------------------------

27

3.2.1 Linear Loads------------------------------------------ 27

3.2.2 Non Linear Loads------------------------------------ 27

3.2.3 Computer Loads------------------------------------ 28

3.2.4 Motor starting loads-------------------------------- 29

3.2.4.1 Shock Load by Electric Motor starting --- 29

3.2.4.2 Alternator KVA Rating determination----- 30

3.2.5 Fluctuating Loads----------------------------------- 30

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INDEX

Description Page 3.2.6 Unbalanced Loads--------------------------------- 31

3.2.7 Servo Loads------------------------------------------- 31

3.2.8 Welding Loads--------------------------------------- 32

3.3 Effect of Environmental Conditions on alternator kVA rating---------------------------------------

33

3.3.1 Ambient Temperature----------------------------- 33

3.3.1.1 Limiting the operating Temperature rise 33

3.3.2 Altitude------------------------------------------------- 34

3.3.3 Load Power Factor--------------------------------- 34

3.3.4 Environment ------------------------------------------ 35

3.4 Deration due to System requirement---------------- 35

3.5 A Typical example on sizing of alternator---------- 35

3.5.1 Customer Requirement--------------------------- 35

3.5.2 Sizing Calculation----------------------------------- 36

SECTION 4 Parallel Operation of alternators

4.1 Parallel operation conditions--------------------------- 38

4.2 Load distribution--------------------------------------------- 39

4.2.1 Voltage droop--------------------------------------- 39

4.2.2 Power Factor Regulation------------------------- 39

4.3 Parallel operation of generators of unequal power------------------------------------------------------------

39

4.4 Operation in parallel with mains----------------------- 40

4.4.1 Important Notes------------------------------------- 40

4.4.2 Droop on resistive Loads-------------------------- 40

SECTION 5 Protection of alternator

5.1 Terminology related to alternator protection----- 42

5.2 Protection relay settings ---------------------------------- 44

4

INDEX

Description Page

5.2.1 Stand alone operation---------------------------- 44

5.2.2 Generator control Relays------------------------ 45

5.2.3 Alternators running in parallel with each other-------------------------------------------------------------

46

5.3 Protection Relays Settings-------------------------------- 47

5.4 Correlation of Circuit Breaker and Protection Relays------------------------------------------------------------

48

SECTION 6 Testing of Alternators

6.1 Standard Factory Tests------------------------------------ 50

6.2 Special factory tests---------------------------------------- 50

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ALTERNATORS

SECTION 1

GENERAL

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GENERAL

1.1 INTENDED USE

‘LSC’ alternators coupled with diesel / gas engines and steam turbines are ideally suited for all applications requiring high quality and high reliability electrical power requirement, for standby, continuous or emergency supply requirements.

1.2 TYPE

LSC alternators are Self Excited, Self Regulated, Brushless type. They have salient pole rotating field with damper cage , armature with short pitched winding , exciter and an electronic Automatic Voltage Regulator (AVR) .

1.3 PRODUCT RANGE

LSC alternators are horizontal foot mounted either with single or double bearing construction, conforming to National and International standards. These are available for Single phase or Three phase supply .The standard product range is:

7.5 - 2850 kVA, 415 V, 3 Phase, 50 Hz, 1500 RPM, DOUBLE BEARING

7.5 -2000 kVA, 415 V, 3 Phase, 50 Hz, 1500 RPM, SINGLE BEARING 4.5 - 30 kVA, 230 V, 1 Phase, 50 Hz, 1500 RPM, DOUBLE BEARING 4.5 - 30 kVA, 230 V, 1 Phase, 50 Hz, 1500 RPM, SINGLE BEARING

1370 – 1910 kVA, 415V, 3 Phase, 50Hz, 1000 RPM DOUBLE BEARING

On request, alternators can also be manufactured and supplied for other voltages, less than or equal to 660 V. For such requirements , the inquires should be referred to Works.


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1.4 STANDARDS

LSC alternators are manufactured to meet requirements of both National and International Standards given below:

Indian Standard IS 4722 : 2001 Rotating Electrical Machines -

Specification British Standard BS :5000(Part 99) Rotating Electrical Machines International Electromechanical Electrical Machines Ratings and Commission IEC :60034-1 Performance

Alternators can also be manufactured according to other standards and specifications. For such requirements, the inquiries should be referred to Works.

1.5 POWER RATING

Power rating in kVA, is specified for continuous i.e. duty S1 according to IS : 4722 on the following standard operating conditions :

• Ambient temperature ≤40° C • Power factor = 0.8 - 1.0 p.u(Lag.). • Installation Altitude ≤ 1000 m MSL

• Practically symmetrical load

For conditions other than the above, the derating / correction factors as explained in section 3 of this manual should be considered. 1.5.1 DUTY “S1” OPERATION: CONTINUOUS As the name suggest, the machine can be allowed to run continuously at constant load upto its rated kVA for 24 Hour 365 days in a year as per the conditions stated on the name plate. 1.5.2 DUTY “SCH” OPERATION: WORKSITE Allow an S1 duty alternator to supply an output of 110% for I hour every 6 hours and which can cause a temperature rise which is higher than the permissible ‘H’ class limits(defined in section 2.3.2). 1.5.3 DUTY “SEC” OPERATION STANDBY

The machine rating defined is standby only and not continuous. In this power rating is around 105% of S1 duty. In standby mode the machine is allowed to be operated intermittently without any over load on standby rating for a max of 500 hours per year but permissible class ‘H’ limits will be exceeded .


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1.6 VOLTAGE & FREQUENCY

Standard LSC Alternators are designed for 415 V terminal voltage and 50 Hz frequency. The alternators are capable of delivering rated output at rated power factor with

• Voltage variation of ± 5 %

• Frequency variation ± 3 % But under no condition the temperature rise will be more than 10 ºC above the specified temperature rise limits (See Section 2.3.2) e.s. in case of LSC alternators where ‘H’ class insulation is used, temperature rise shall be limited to 135 ºC instead of 125ºC over an ambient of 40 ºC. It is however to be understood that continuous operation under these conditions has an effect on the life of insulation.

1.7 SPEED

LSC alternators of 4 pole -design are suitable for operation at : • 1500 RPM for 50 Hz supply frequency or • 1800 RPM for 60 Hz supply frequency

LSC alternators of 6 pole -design are suitable for operation at :

• 1000 RPM for 50 Hz supply frequency or • 1200 RPM for 60 Hz supply frequency

1.8 EFFICIENCY

The alternator is driven by a primer mover. The mechanical power from the primer mover is converted into electrical power. In order to match the size of the prime mover for a given alternator, the efficiency of the alternator should be known.

The efficiency is defined as :

Out put in kW Out put Efficiency = = Input in kW Out put + losses


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ALTERNATORS

SECTION 2

‘LSC’ ALTERNATORS FEATURES


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‘LSC’ ALTERNATORS FEATURES

2.1 QUALITY

LSC alternators are manufactured in the most modern manufacturing unit of “Leroy Somer & Controls India (P) Ltd” at Noida (U.P.) using state-of-art manufacturing / testing equipments and well proven processes thus ensuring highest level of quality and reliability. 2.2 SALIENT MECHANICAL FEATURES

2.2.1 STATOR FRAME

The stator frame is fabricated with standard steel , designed to ensure proper distribution of air flow over core and winding.

LSC alternators are designed to give high efficiency at all loads of operation because they are :

Manufactured with Low loss, High quality, Burr free, Cold rolled stampings Have generous Electrical and Mechanical design.

2.2.2 ROTOR CORE Rotor core is made of high quality low content silicon steel popularly known as salient pole construction. The poles carries continuous damper winding. 2.2.3 DYNAMIC BALANCING

To ensure minimum vibration during operation, all the alternator rotors are dynamically balanced as per ISO :1940/1 grade 2.5. Double bearing rotors are balanced with half Key.

2.2.4 TERMINAL BOX

Terminal box is located on top of the alternator with generous space inside for easy termination of cables.


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2.2.5 BEARINGS

LSC standard alternators upto 250KVA are provided with bearings having permanent lubrication; above 250KVA externally lubricated grease bearings are provided. Specified life of bearings is around 30,000 hours when operated as per specified conditions .

2.2.6 COOLING

The purpose of cooling system is to remove the heat generated inside the alternator and to limit the temperature rise to permissible limits.

All LSC alternators have cooling method IC – 01 as per IS :6362

The cooling requirements of STANDARDS are fully satisfied by providing an efficient unidirectional shaft mounted fan on drive end, which takes surrounding air from non-drive end and the hot air freely get discharged to the medium surrounding the alternator from drive end. 2.2.7 TROPICALISATION With use of proper grade of insulating material and insulating resin, LSC alternators are fully tropicalised. This is achieved by use of :

• Insulated Copper winding wires of temperature class 200°C

• High grade multi- layer insulating sheets to insulate windings of main

machine as well as exciter .

• VPI (Vacuum Pressure Impregnation) in class ‘H’ insulating resin, and

• Epoxy Gel coat on critical winding parts.

However, in costal area where condensation occurs due to high humidity, in order to avoid water condensation, Anti - Condensation Heaters ( space heaters) need to be fitted in the alternator. The purpose of the heater is to keep windings of the alternator warm when it is not running and therefore prevent lowering of the insulation resistance below safe values.

LSC alternators can be provided with Anti - Condensation Heaters on request at EXTRA COST.


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2.2.8 ENCLOSURE The LSC alternator is provided with an enclosure as per IS : 4691 to prevent : • Accidental contact with rotating parts

• Accidental contact with live parts

• Ingress of solid foreign bodies

• Harmful ingress of liquids.

The degree of protection for the enclosure is designated by the code IP( Index of

Protection) . This is followed by two numerals which indicates various degree of protection given in standards are reproduced below.

1st Numeral 2nd Numeral 0 No protection 0 No protection 1 Protection against solid objects 1 Vertically dripping water shall have greater than 50 mm (Eg : Hand) no harmful effect 2 Protection against solid objects 2 Protection against dripping of water greater than 12 mm (Eg : Finger) at up to 15° from the vertical 3 Protection against solid objects 3 Protection against water falling at greater than 2.5 mm upto 60° from the vertical (Eg: Rods, screw driver) 4 Protection against solid objects 4 Water splashed from any direction Greater than 1.0 mm shall have no harmful effect

Standard LSC Alternators are with IP-23 degree of protection for the enclosure, which is superior to IP-21 & IP-22


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2.2.9 MOUNTING

LSC alternators are available in double bearing as well as in single bearing versions depending upon the prime mover requirement . Double bearing alternators are horizontal foot mounted B3 construction .Single bearing alternators are available in following types of SAE Flanges and coupling disc combinations .

Coupling Disc

kVA Rating Flange 7.5 10 11.5 14 18

7.5-25

SAE 3 SAE 4 SAE 5

√ √

√ √

√

30 - 50 SAE 2 SAE 3

√ √

√ √

62.5 - 125

SAE 1 SAE 2 SAE 3

√ √

√ √

√

140 - 250 SAE 1 SAE 2

√

√

320 - 500

SAE 0 SAE 1 SAE 2

√

√ √

625 - 1010

SAE 0 SAE 1

√ √

√

1250 - 2000†

SAE 0

√

† SAE size 00/21 is available at request.


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2.3 SALIENT ELECTRICAL FEATURES 2.3.1 POWER FACTOR

‘LSC’ Standard alternators are suitable for all industrial applications and the kVA rating is defined for 0.8(lagging) power factor loads . These alternators are also suitable for operation with loads other than the standard 0.8(lagging) conditions , for such conditions derating / correction factor need to be used. (See Section 3)

2.3.2 INSULATION CLASS

When running on load, the alternator generates heat . The difference between the alternator winding temperature and the ambient temperature is termed as “ Temperature Rise”. For healthy operation of the alternator , this temperature rise has to be kept within permissible limits . This limit depends on the type of insulation materials used and the surrounding air temperature where the alternator is working. Standards specify the limits for this ‘temperature rise’ based on ambient air temperature and the class of insulation used.

The internationally accepted standard ambient air temperature reference is 40 °C.

The table below gives the operating temperature limit, permissible temperature rise limit and temperature margins for different insulation classes, with the ambient air temperature of 40°C.

• Insulation Class F H

• Permissible Temperature Rise 105°C 125°C

(over 40°C ambient)

• Operating Temperature Limit 155°C 180°C

• Temperature Margin Left 10°C 15°C

‘LSC’ alternators are manufactured with class ‘H’ insulation which has better temperature margin as compared to class ‘F’ insulation


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2.3.3 EXCITATION SYSTEM With over 100 years of experience Leroy Somer have designed and developed a perfect excitation system for entire range of alternators.

2.3.3.1 Principle of operation

During starting , the residual magnetism in the exciter stator creates a current in the

exciter armature(1).This current is rectified by the rotating diodes(2) and feeds the main field(3) . The induced voltage is then used to increase the excitation power via the AVR(6) to the exciter field (5) to ensure a fast and smooth build up of the out put voltage in the main stator winding(4)

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3

1

5

(4)

The sensing voltage for the AVR is taken from the output terminal leads. Two types of excitation systems used in LSC alternators are :

1) Shunt Field excitation system 2)AREP excitation system.

2.3.3..2 Shunt Field Excitation :

The alternators upto 250KVA are with shunt field excitation system and electronic

Automatic Voltage regulator : AVR R238 . The regulator monitors the excitation current as a function of the alternator output voltage .

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(2) ►▌

(6)

SHUNT EXCITATION

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2.3.3.3 AREP Excitation System With AREP Excitation, electronic Automatic Voltage Regulator : AVR R448 or R 449 is

powered with two AREP(Auxiliary) windings which are independent of voltage detection circuit. The first winding has a voltage proportionate to the output voltage of the alternator (shunt characteristic) and the second has a voltage in proportion with the stator current (Compound characteristic , Booster effect ).

The power supply voltage is rectified and filtered before being used by the

regulator monitoring electronic circuit.

AREP EXCITATION SYSTEM

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AVR. R-448 / R-449

▲ ▲ ▲ ▲ ▲ ▲

A.V.R. R238

▲ ▲ ▲ ▲ ▲ ▲

AREP excitation offers following advantages

• Ability to sustain short circuit current • Improved motor starting Characteristics • Better Voltage Regulation even under unbalanced Loads

2.3.3.4 PMI Feature

In LSC alternators the exciter field (stator) is also provided with PERMANENT

MAGNETS. Therefore, the process of initial voltage build up is very positive as residual magnetism is hardly ever dependent upon long idle time.

2.4 AREP WINDING AND SHORT CIRCUIT WITHSTAND CAPABILITY In LSC alternators above 250KVA, two independent windings ( Teflon

insulated ) are embedded in the stator alongwith main stator winding. Therefore, when the alternator is run at rated speed, the main winding generates the rated voltage of 415 volts whereas the AREP winding independently generates its own voltage/current and feeds the AVR.

In the event of 3 phase short circuit, the terminal voltage becomes zero but the

AREP winding voltage is continues powering the AVR. Therefore, the AVR does not stop functioning. AREP winding feeds the short circuit power through exciter to main rotor winding and thereby the short circuit current is supplied. This Short- circuit current of three times (which is decaying in nature) is maintained for about 10 Secs thereby giving sufficient delay to trip the circuit breaker .

All LSC Alternators 320 KVA & above are provided with AREP winding.

Although LSC alternators upto 250KVA are with the shunt field excitation system, if the customer requires these alternators can be provided with AREP feature as optional .

2.5 VOLTAGE ADJUSTMENT RANGE

Standard LSC Alternators are designed for Voltage adjustment range of ±5% of

rated terminal voltage. The voltage variation of ±10% can be achieved by EXTERNAL POTENTIOMETER. This potentiometer should be put across defined terminals of AVR after removing shorting links.

Alternators with voltage adjustment range of ±10% can be supplied on

special request. 2.6 VOLTAGE REGULATION

The AVR’s used in LSC Alternators ensure the voltage regulation better then ±1.0%.


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2.7 VOLTAGE WAVE-FORM The wave shape of the voltage generated by the alternator is very close to a

sine wave. Due to the presence of harmonics, the wave shape deviates from the pure sine wave. The purity of voltage wave form is expressed in the form of ‘Distortion Factor’.

When power lines are running in the proximity of telephone lines, a coupling effect

is produced; the harmonics in the power line cause a noise in the telephone circuit. This is known as Telephone Harmonic Factor (THF) or Telephone influence factor(TIF).

The geometry of the magnetic circuit and the proper selection of short pitched

armature winding results in the generation of practically a virtual sine-wave. voltage. • Telephone Influence Factor “TIF”

The IEC, IS, BS requirements are easily satisfied by LSC alternators.

• Total Harmonic distortion

≤ 3.0% under balanced load

2.8 TRANSIENT VOLTAGE DIP (TVD) The alternator voltage is controlled by AVR . On application of a sudden load,

the terminal voltage of the alternator dips momentarily outside the voltage regulation band and will recover to nominal value after a short time delay. The amount of voltage dip depends on the magnitude of the sudden load and its power factor. The initial voltage dip is termed as Transient Voltage Dip (TVD) and time taken to recover within the regulation band is termed as recovery time. In LSC Alternators , the magnetic circuit and the windings are optimised for low Transient Voltage Dip (TVD) of 14 - 20% on full load at 0.8 PF.

The rate of voltage change depends on the time constants of alternator, exciter machine and the AVR. In LSC Alternators, recovery time is ≤ 1 sec. because of generous exciter design.


-117-

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2.9 RADIO INTERFERENCE Since the LSC alternators are Brushless type with proven AVR. the low levels of

interference is achieved. 2.10 OVER LOAD CAPACITY OF LSC ALTERNATORS : Permissible over load for LSC alternators is as given below :

• To adapt to the requirements of internal combustion engines, an overload of 1.1 times the rated current can be maintained for 1h after every 12 hours of operation.

Normally this does not become a practical proposition as at customer

site such a control is difficult to implement. Therefore it is a good practice to avoid overloading .

• Short-term over load capacity

1.5 times of rated current for 30 Seconds and 3 times of rated current for 10 Seconds is available for starting currents of induction motors.


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2.11 AUTOMATIC VOLTAGE REGULATOR The Automatic Voltage Regulator (AVR) is a standardised module. The main

function of AVR is to precisely regulate the terminal voltage of the ALTERNATOR and provide under-speed protection for safe operation during low speed running of prime mover. AVR takes the input power supply from the main winding for alternators upto 250KVA and through AREP winding in case of alternators 320KVA & above . It senses the two phase voltages and compares with the reference voltage to adjust exciter field current until desired output voltage is developed.

LSC AVRs have following features :- • Voltage regulation accuracy of ± (0.5 to 1) % from No load to Full load

• 2 phase sensing for better regulation under Asymmetric / Unbalanced load condition

• Under Frequency Roll Off (UFRO) to avoid over excitation in field winding when prime mover is running at low speeds.

• Built- in filters , suitable for non linear loads.

• AVR R-448 and R-449 are suitable for parallel operations

• External voltage adjustment facility upto ± 10 % of rated voltage

• Compact design with Fully potted for better reliability against humid and

corrosive atmosphere

• High quality imported components for long service life

• Fuse is provided as protection against wrong operation.

• Mounted on Anti vibration mounts

2.11.1 TYPE OF AVRs

• AVR R-238 : 7.5 - 250 kVA standard alternators have AVR R-238 and it is suitable for solo operation

• AVR R-448 : standard alternators of 320 to 1250 kVA have AVR R-448 and it is suitable for both solo and parallel operation for lower ratings it can be provided as optional provided asked for at order stage

• AVR R-449 : standard alternators of 1500 KVA and above have R-449 and it is suitable for both solo and parallel operation.


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2.11.2 TECHNICAL DATA

2.11.2.1 AVR – R238

• Power supply : 240V – 50Hz • Load Current : 3 A D.C. • Electronic Protection (Over load , voltage detection : Terminal voltage reduces to 100V opening , short circuit) • Voltage détection : 2VA isolated via internal transformer • Voltage regulation : +/- 1% • Response time : 500 ms • UFRO : 48 to 42 Hz , threshold adjustable through trimmer. • Temperature : operating 0 to 75 ºC • Volt Adjust : +/- 10% ,by adding 20 KOhms external potentiometer

2.11.2.2 AVR - R448 • Power supply : max 140V – 50Hz • Load Current : 6 A D.C. • Electronic Protection (Over load , voltage detection : Excitation over load current for 10s then opening , short circuit) : return to approximately 1A • Voltage detection : 5VA isolated via internal transformer • Voltage regulation : +/- 1% • Response time : 500 ms • Voltage adjustment : +/- 10% by adding external potentiometer of 1KOhms • UFRO : 48 to 42 Hz , threshold adjustable through trimmer. • Temperature : operating 0 to 75 ºC • Load Acceptance Module ( LAM) : yes • Along with AREP winding : capable of providing short circuit current.

2.11.2.3 AVR- R449

• Power supply : max 140V – 50Hz • Load Current : 7 A D.C. • Electronic Protection (Over load , voltage detection : Excitation over load current for 10s then opening , short circuit) : return to approximately 1A • Voltage detection : 5VA isolated via internal transformer • Voltage regulation : +/- 1% • Response time : 500 ms • Voltage adjustment : +/- 10% by adding external potentiometer of 1KOhms • UFRO : 48 to 42 Hz , threshold adjustable through trimmer. • Temperature : operating 0 to 75 ºC • Load Acceptance Module ( LAM) : yes • Along with AREP winding : capable of providing short circuit current. • Additional Module : R-731 for power factor regulation when parallel with mains.


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2.11.3 SPECIAL FEATURES OF AVR R-448 Load Acceptance Module(LAM) on application of a load , the rotation

speed of the alternator decreases .When it passes below the preset frequency ,threshold, the LAM causes the voltage to drop by approximately 15% and consequently the amount of active load applied is reduced by approx. 25% , until the speed reaches its rated value again.

Hence the LAM can be used either to reduce the speed variation and its

duration for a given applied load OR to increase the applied load possible for one speed variation.

To avoid voltage oscillation , the trip threshold for the LAM function should

be set approximately 2 Hz below the lowest frequency in steady state.

In none of the AVR’s presently available in the market ,LAM feature is available , this feature is very useful when starting a large size motor on D.G.

AVR R-448 is immune to voltage distortion caused by non linear loads and as such

no external filters are required. A special fuse is provided to disconnect AVR power supply in case of over

excitation thereby protecting the armature and associated equipments. 2.11.4 SPECIAL FEATURES OF AVR R449 In addition to features of AVR R448 , AVR R449 has following features One additional module called R-726 can be connected for parallel operation

with grid to maintain the power factor . This feature can also be used when such alternators are parallel with large alternators in the captive power stations where It is necessary to control the power factor of smaller alternator to avoid over loading of excitation system.


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2.11.5 UNDER-FREQUENCY-ROLL-OFF (UFRO) There is an in-built Under Frequency Roll Off (UFRO) feature in all Automatic

Voltage Regulators which reduces the terminal voltage linearly with speed below a presetable threshold (for example, 47.5 Hz for 1500 RPM machines). This protects the field circuit from over excitation when DG set is running at low speeds.

UFRO function is displayed by LED in AVR R-238. 2.11.5 DIODE FAILURE MONITOR This unit can be supplied on extra cost to monitor failure of any of the rotating

Rectifiers in case of Alternator 320 KVA and above.


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25

ALTERNATORS

SECTION 3

SIZING OF ALTERNATORS


26

SIZING OF ALTERNATORS

3.1 STANDARD RATINGS OF LSC ALTERNATORS Brush less ,self excited, self regulated 1500 rpm , 415V ,50 Hz , suitable for ambient

temperature of 40 deg. C and altitude less than 1000 meters, Protection IP23, Voltage regulation +/-1% , Class of Insulation ‘H’ and the temperature rise as per ‘H’ Class insulation Limits.

THREE PHASE STANDARD RATINGS AND FRAME SIZE

SINGLE PHASE RATINGS AND FRAME SIZE

kVA Rating Frame Size

7.5 LSC 28VS1 10 LSC 28VS2

12.5 LSC 28S1 15 LSC 28S2 18 LSC 28M 20 LSC 28L 25 LSC 33S2 30 LSC 33M


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kVA Rating Frame Size 10 LSC28VS2 15 LSC28S1 20 LSC28S2 25 LSC28M 30 LSC28L 35 LSC33S1 40 LSC33S2 45 LSC33S3 50 LSC 33M

62.5 LSC 33L1 75 LSC 33L2

82.5 LSC 39S1 100 LSC 39S2 125 LSC39M 140 LSC39L1 160 LSC39L2 180 LSC 45S1

kVA Rating Frame Size 200 LSC45S2 250 LSC45M1 275 LSC45M2 320 LSC45L 380 LSC54S2 450 LSC54S4 500 LSC54M1 550 LSC54M2 600 LSC54L 625 LSC62S 750 LSC62M 1010 LSC62L 1250 LSC74M 1500 LSC74M 2000 LSC74L 2450 LSC86L 2850 LSC 86L

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3.2 EFFECT OF DIFFERENT LOADS ON ALTERNATOR kVA RATING The types of load encountered by an alternator can be broadly classified as

3.2.1 LINEAR LOADS Linear Loads can be identified from following characteristics :- • Load impedance is always constant regardless of the applied voltage • The alternator current increases proportionately as the voltage increase

and decreases proportionately as the voltage decreases. Examples of linear loads are motor, incandescent lighting and heating loads. Selection of alternator for these load applications does not pose any

problem. Hence no deration is required for this type of loads. Considering the maximum connected load and average load which remains all the time connected, suitable rating of alternator can be arrived at. This output rating of alternator must be corrected for non- standard operating conditions.

3.2.2 NON LINEAR LOADS In Non linear loads the load current is not proportional to instantaneous voltage

and often the load current is not continuous. They generate harmonics in their current wave form which in turn lead to distortion in alternator voltage wave form.

To minimize the resulting losses in the alternator and the equipment as a whole and

to keep connected equipment functioning properly, the harmonic content of the voltage waveform should be kept as small as possible. This is done through efficient winding design, slot configuration and proper skew.

A low sub-transient reactance x”d is required for this purpose. This is realized by using a suitable dimensioned damper cage in the rotor of LSC alternators.


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`

The derating factor for various types of non- linear loads as applicable to LSC alternators are as follows:

Type of Non-Linear Load Derating Factor a) Fluroscent lighting load No deration b) UPS & Telecom load controlled by No deration 12 Pulse Thyristor bridge with filter c) UPS & Telecom load controlled by 70 % 6 Pulse Thyristor bridge with filter d) UPS & Telecom load controlled by 35 % 3 Pulse Thyristor bridge with filter e) Variable speed DC/AC drive 50 % 6 Pulse Thyristor bridge controlled f) Induction Furnace load 70 % 6 Pulse Thyristor bridge controlled Example : For ‘X’ kVA non-linear 6 pulse thyristor telecom load and ‘Y’ kVA linear load ,the

suitable alternator rating shall be :-

Selected Rating of Alternator in kVA = ( X / 0.7 ) + Y 3.2.3 COMPUTER LOADS

Computer loads are very sensitive to the characteristic of voltage variation,

frequency variations, harmonic contents, voltage unbalance etc, of power supply. If these characteristics do not match with the stipulated figures, malfunctioning of computers may take place. Under these conditions care should be taken to see that there are no motor loads/ step loads / non- linear loads which will cause the transient voltage dip/rise and harmonics which may not be acceptable to the computer loads, hence it is advisable to have separate DG sets for computer loads.

Following information is required for selecting a suitable Alternator for these load

applications : • Total kVA of computer load and its operating P.F.

• Acceptable steady state and transient state voltage variation

• Acceptable values of total individual harmonic content

• Allowable frequency variation (Engine requirement)


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3.2.4 MOTOR STARTING LOADS When Induction Motor is started, it draws heavy current from the power source,

which is known as Starting Current or locked rotor current of induction motor and, the alternator experiences a Shock Load during starting period. This causes Voltage Dip in the alternator terminal voltage. It this voltage dip is higher than the holding voltage of the contactors or circuit breakers normally used, the other Base loads connected to this alternator will automatically get switched OFF due to tripping of CB during starting of motor .

Transient Voltage Dip ≤ 20 % is essential to keep the other base loads operating

satisfactorily during starting of Induction Motors . Thus, the following aspects are required to be taken into account while selecting

the Genset suitable for three phase Motor Starting Loads : • Rating of the motor / motors • Type of motor (slip ring / squirrel cage)

• Type of load connected to motor i.e. high inertia

• Method of starting

• Rated full load current

• Starting current and power factor

• Restriction on Transient Voltage Dip

• Frequency of starting

• Base load at the time of starting induction motor

• Any other load apart from the motor loads :

• Sequence of starting of motors

3.2.4.1 Calculation of shock load caused by Electric Motors on starting :

S1 = UN x IN x 1. 73 , whereS1 = Nominal motor input (kVA) UN = Nominal voltage (V) IN = Nominal current (A) dS = K x S1 , where K = ratio of Starting current to normal current .Typical values of K K = 5 to 7 times of FLC for squirrel cage motors DOL starting = 2.5 to 3.5 times of FLC for squirrel cage motors star delta starting = 1.5 to 2.0 times of FLC for slipring (induction) motor = 2 to 3 times of FLC for auto transformer starting at 65 % tappings = 3 to 4.5 times of FLC for auto transformer starting at 85 % tappings


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3.2.4.2 Alternator kVA Rating determination The suitable rating of alternator can be selected according to the required

nominal ouput ( = total of consumer inputs S1 ) taking into account any necessary derating factors as explained earlier.

The alternator rating thus determined can be used if : • the maximum shock load is equivalent to no more than 110 % of the

Alternator kVA rating

Note : In case TVD restriction of 20% is not applicable and the load connected to the motor are not with heavy inertia, following chart can be used as reference.

Type of Starter Starting Current Required alternator kVA Direct On Line 6 Times Rated Full Load 2.5 Times Motor HP or

3.3 Times Motor kW Star Delta 3 Times Rated Full Load 1.25 Times Motor HP or

1.6 Times Motor kW Rotor Resistance 2 Times Rated Full Load 0.85 Times Motor HP or

1.1 Times Motor kW Autotransformer :-

Tapping at 65 % 2.5 Times Rated Full Load 1.1 Times Motor HP or 1.5 Times Motor KW

Tapping at 80 % 4 Times Rated Full Load 1.7 Times Motor HP or 2.3 Times Motor kW

As a general reference For “Lift Operation” Alternator kVA rating shall

be minimum 3 times of motor HP rating

3.2.5 FLUCTUATING LOADS

Some times alternators are to be sized for wide fluctuating current i.e. furnaces ,

cranes, cutter, Lifts etc. For such cases it is necessary to size the alternator based on peak current and not on the average current. When the load on the alternator is continuously fluctuating say 90% to 110% or more than for sizing the alternator the upper limit i.e. 110% should be considered.

Generally such load will also have power factor lower than 0.8, and will also

generate harmonic distortion. Hence it is necessary to consider derating factor due to lower power factor as indicated in section 3.2.3 in addition to sizing corresponding to peak current. If the fluctuating load is more than 10% of total load it is also necessary to consider deration due to harmonics generated.


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3.2.6 UNBALANCED LOAD On a three phase Alternator, if the loads are not equally distributed in all the three

phases , then the alternator is said to be feeding an unbalanced load . This unbalance occurs in practice due to the single phase loads being applied across one or two phases of the three phase Alternator . The effect of unbalanced loading is that the field winding of the Alternator gets over - heated due to negative sequence currents and the voltage regulation worsens.

To avoid this problem , it is advisable to distribute the single phase loads on all three phases equally.

If loads in the form of different currents are imposed on the other lines, the values of the positive - sequence, negative - sequence and zero - sequence must be determined analytically or graphically in order to determine the actual load on the alternator.

The electrical design of the LSC Alternator permits :

• 60 % of the nominal current at 0.8 p.f. or above as a single phase load between phase and neutral.

• unbalanced load of upto 20% at 0.8 p.f. or above of its rated load without exceeding the rated current in any of the phases beyond full load current of the Alternator.

Moreover, this unbalance will cause circulating currents which will flow through

the neutral conductor when the alternators operate in parallel and therefore would cause difficulties in smooth parallel operation.

3.2.7 SERVO LOADS

The textile and paper mills normally have sensitive group driven equipments and at such places conventional voltage stabilizer of capacity 50 to 100KVA are being used . These stabilizers basically use transformer for constant output voltage irrespective of variation in input voltage. When such stabilisers are being fed power from a generator

• At the time of starting it draws high inrush currents • Due to these inrush currents there is a considerable voltage droop during

switching on and the circuit breaker may trip.

In general , the largest size of stabiliser which can be charged is approximately 50% of alternator rating .


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3.2.8 WELDING LOADS Welding loads are intermittent type of loads . The input kVA indicated on the

name plate of the welding machine is average RMS Power . The peak Power while striking the arc is higher than the name plate data. Due to varying nature of load ,while operating , the power factor of the welding machine is low as 0.6 . Hence derating factor should be applied as per section 3.3.3.

At Large construction sites where major loads constitutes welding loads the

alternator should be sized as follows

• Add total KVA load of all welding machines as per name plate rating • In general , considering the lower power factor impact and the name

plate rating as RMS power , a derating factor of 0.5 is applicable for sizing an alternator for welding loads.

Total Welding KVA Alternator KVA rating = --------------------------- + Normal load KVA 0.5 • The welding load should be distributed in such a manner so that

unbalance current does not exceed 20% of rated current.


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3.3 EFFECT OF ENVIRONMENTAL CONDITIONS ON ALTERNATOR kVA RATING

Alternators are designed for certain standard specifications as described in section 3.1. In case the site conditions differ from the standard conditions than alternators needs to be derated / rerated.

3.3.1 AMBIENT TEMPERATURE

For applications where the ambient air temperature is greater than 40ºC, the alternators must be derated to ensure that the actual temperature rise does not exceed the permissible limits as specified in standards. Standard kVA ratings are specified at 40ºC. These output kVA ratings must be multiplied by the derating factors given below for other temperature conditions.

Ambient Temp.

ºC 10 20 30 40 45 50 55

Derating Factor 1.1 1.08 1.04 1.0 0.96 0.93 0.91

For example, 100 kVA standard alternator when operated at ambient temperature of 45°C, can deliver 0.96 x100=96 kVA satisfactorily. 3.3.1.1 Limiting the Operating Temperature rise to a lower insulation class The standard kVA ratings for LSC alternators is specified by temperature rise limited to class ‘H’ insulations conditions. The cases may be where the customer specifies that the temperature rise should be limited to class ‘F’ or class ‘B’ insulation limits . In such cases , the standard output can not be taken from alternator and deration factor has to be considered . The Table “PERMISSIBLE RATING UNDER VARIOUS CONDITIONS” gives the derated kVA power obtainable for various ambient temperatures when temperature rise is also to be limited to class ‘F’ or class ‘B’ insulation limits.


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3.3.2 ALTITUDE

The air takes away the heat generated from inside the alternator . As the altitude increases the density of air decreases. This results in higher temperature rise inside the alternator.

Upto an altitude of 1000m above mean sea level, the change in the density of air Is insignificant and does not change the heat transfer properties. Hence, all industrial alternators are designed for operation suitable upto 1000m altitude. If it is required to operate the alternator above 1000m altitude, then the alternator has to be derated as given below:

Altitude (meters) 1000 1500 2000 2500 3000 3500 4000

Derating Factor 1.0 0.96 0.93 0.91 0.88 0.85 0.82

For example, a standard 1000 kVA alternator when operating at altitude of 2000 m. above sea level can deliver 0.93x1000=930 kVA successfully.

3.3.3 LOAD POWER FACTOR

Alternators have no control over the power factor of the load it supplies. The kVA rating specified corresponds to standard 0.8 (lagging) power factor conditions. Lower power factor demands a higher excitation and results in increased heating of the field winding and exciter.

For lower power factor operation, the alternator has to be derated as below

Lagging P.F. 1 0.9 0.8 0.7 0.6 Derating factor for Power

Factor 1 1 1 0.92 0.84

Prime movers are, as a standard, matched to the alternator out put at 0.8 power factor (lagging). At higher power factors, the engine limits the kW out put.

Leading power factor of loads causes a reduction of excitation current. However instability and rapid voltage rise can be caused by large capacitive loads. Therefore the power factor improvement capacitors should be switched OFF to avoid instability and rapid voltage rise.


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3.3.4 ENVIRONMENT

Environment conditions under which an alternator has to work are :

• Atmosphere charged with chemical fumes

• Saline atmosphere

• Dust or sand laden atmosphere

When an alternator has to operate in a atmosphere having chemical fumes or a saline atmosphere, the windings and other parts of the alternator have to be given a special protective treatment .

Under site conditions where the air may be heavily laden with fine dust or sand

alternator must be fitted with AIR FILTERS at inlet. The sizing of these alternators is important to avoid airflow restrictions and advice should be sought from the Works so that suitable deration factor can be worked out.

3.4 DERATION DUE TO SYSTEM REQUIREMENTS In normal case alternators are designed for 415V ,50Hz , 3phase system for giving 100% output under the standard site conditions. In case, the same alternator is allowed to run at different system voltage and frequency(standard site conditions), than the allowed output of alternator shall be as per the table given below

OUT PUT % at Voltage Frequency

50HZ Frequency

60HZ 380 92 100 400 100 105 415 100 109 440 92 114 460 NA 118 480 NA 120

3.5 A TYPICAL EXAMPLE ON SIZING OF ALTERNATOR

3.5.1 Customer Requirement : A customer XYZ asks for a D.G. set for the following loads & site conditions:

• Total A.C. Motors connected = 200HP • D.C. Drive load =100Kw • Welding Loads =10Nos. each of 10kVA • Lighting Load =20kw • Fluctuating Load =25kVA to 100kVA

The generator has to work at site where ambient temperature is 50 deg.C altitude is 900 mtrs and although alternator is having ‘H’ class insulation However the temp. rise should not be more that ‘F’ class limits. Running Power factor is 0.85 (lagging) System requirement is 415V+/- 5% ,3phase 50Hz 4 wire


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3.5.2 Sizing Calculation : For sizing alternator under above conditions following steps should be taken. Step 1 : Convert all loads to equivalent kVA considering 0.8p.f. and respective

efficiency. • Motors load of 200HP = 200 x 0.746 / 0.80 x 0.85 = 220kVA (Considering efficiency 85%) • D.C.Drive Load100kW =100 / 0.80 x 0.85 = 147kVA (Considering efficiency 85%) • Welding Loads = 10 x 10 / 0.82

= 122kVA (Considering efficiency 85%) • Lighting load = 20/ 1 = 20kVA ( As power factor is unity ) • Fluctuating Load = 100kVA

TOTAL kVA CONNECTED = 609kVA

Step 2 : Write derating factor of each load and site conditions

• Motor load = NIL as no TVD restriction • D.C. Drive load = 0.5 • Welding loads = 0.5 • For 50deg.C ambient temp. = 0.93 • For Temp. rise as per ‘F’ class = 0.85 • For altitude 900mtrs =NIL • For running P.F. 0.85 of load =NIL

Step 3 : Devide the kVA calculated in step 1 individually in order to calculate of total kVA demand due to different type of loads.

• Motors load of 200HP = 220/ 1 = 220kVA • D.C.Drive 100kW =147 / 0.5 = 294kVA • Welding Loads = 122 / 0.5

= 244kVA • Lighting load = 20/ 1 = 20kVA • Fluctuating load = 100kVA

TOTAL kVA Demand by different loads = 878kVA Step 4 : Apply the derating factor one by one for each site condition on the total kVA demand by different loads.

• For Ambient temp. of 50 deg. C = 878 / 0.93 = 944kVA • For limiting temp. rise as per’F’ class limit = 944 / 0.85 = 1110kVA • For altitude 900 mtrs = No deration

Hence TOTAL kVA Demand for specified loads shall be = 1110kVA Nearest standard Rating of alternator available to this is 1250kVA hence

1250kVA alternator is to be selected for this load & site requirement.


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ALTERNATORS

SECTION 4

PARALLEL OPERATION OF ALTERNATORS


38

PARALLEL OPERATION OF ALTERNATORS

It is now a common practice to run generating sets in parallel. Depending upon

load, parallel operation of the appropriate number of generating sets means optimum loading and high efficiency resulting in improved economy. In addition, it increases the operating safety of the system, since if any one of the set fails , the appropriate amount of load can be taken on by the other sets .

Even though parallel operation of alternators is commonly used, it is also experienced world over that maximum failure of alternators takes due to inadequate paralleling system and defects there in.

4.1 PARALLEL OPERATION CONDITIONS When generators are running in parallel it is necessary to pay attention to its

governing system & regulating system then only the system can run in stable condition which is indicated by proportional sharing of kW and kVAR. Synchronization of two power generating sets means the coupling of their respective phases with each other before coupling the phases following conditions must be filled to match the two wave forms.

• Voltage Balancing : Absolute voltage difference between the running

system and incoming system must be as low as possible. Generally allowed tolerance is +/- 2% of rated voltage. Higher voltage difference result in sudden large magnitude of reactive power flow between the two systems. To prevent generating set from damage due to high reverse reactive power ,reactive reverse power relay with time delay should be used in panel.

• Phase sequence : To ensure the correct phase sequence of both the system before closing the breaker phase sequence must be checked either by installed phase sequence protection relay or by meters before proceeding for first synchronization . closing of breaker with wrong synchronization shall result in damage in generating sets and coupling.

• Frequency balancing : Frequency difference between the running system

and incoming system must be as low as possible. Generally allowed tolerance is +/- 0.2HZ . Higher difference will result in sudden large magnitude of active power flow between the two systems and may also result in higher phase angle error of the due to higher floating frequency. To prevent generating set from damage due to high reverse active power active reverse power relay with time delay should be used in panel.


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• Phase angle difference : At the time of synchronization the max. allowed

phase angle difference is +/- 7 degrees. This should be taken care by checking synchronizing relay and is indicated on the synchroscope.

After connecting together, the active power and reactive power distribution should be balanced.

4.2 LOAD DISTRIBUTION • Active power load distribution is governed by the speed behaviour of the

prime mover. • Reactive load distribution is governed by the alternator voltage

characteristic. The following methods of reactive load distribution may be used : 4.2.1 VOLTAGE DROOP The importance of droop setting can not be over emphasised for stable

operation . The active power distribution is governed by governor of prime over and the reactive power distribution is governed by the voltage regulator (AVR).The slight difference in droop settings either in governor droop setting or in AVR droop setting will create large difference and will make the system unstable.

Generally in captive power station when generators are not parallel with grid,

speed droop of 4% and voltage droop of 3% will maintain stable parallel operation The droop of 3 % is set by the factory at rated current and power factor 0.1. This value is suitable for stable parallel operation .The droop can be adjusted steplessly from 0 - 6 % of nominal voltage depending upon site requirements.

4.2.2 POWER FACTOR REGULATION

This method is used for parallel operation with the mains where high voltage fluctuations occur. An additional regulator module for power factor controller energises the R449 voltage regulator of the alternator in order to maintain the selected power factor, i.e. the alternator voltage is automatically adjusted to the mains voltage.

4.3 PARALLEL OPERATION OF GENERATORS OF UNEQUAL POWER Droop behaviour must be identical. Reactive power is then distributed

according to the ratio between the generators nominal power rating.

LSC Alternators are suitable for parallel operation with alternators of other makes provided necessary droop is available .


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4.4 OPERATION IN PARALLEL WITH THE MAINS The number of generating sets operating in parallel is of no significance.. In most

cases grid supply has a far higher short-circuit capacity, so that the sets running in parallel do not exert any significant influence.

Main voltage variation dU ≤ 2 %. In this case, parallel operation with droop takes place. Main voltage variation dU > 2 % and up to ± 10 % An additional power factor controller module in the alternator or switchgear,

energises the R-449 voltage regulator of the alternator in order to maintain the selected power factor, i.e. the alternator voltage is automatically adjusted to the mains voltage. If a particular power factor is required at the mains point of supply , the current transformer acting on the power factor regulator must be located at this point of supply.

4.4.1 IMPORTANT NOTES : WRONG SYNCHRONISATION It is advisable that synchronisation of two or more sets should be done by trained personals only , as in most of the cases , wrong or improper synchronisation results in major damages to the equipment. A wrong synchronisation is similar to phase to phase fault at alternator terminals. If manual synchronisation is done, than ‘check synchronisation’ relay should be installed and if automatic synchronisation is done then it should not be over ridden due to delay in synchronisation or ‘fail to synchronise’. It is necessary to install reverse power relay.

Neutral conductor current When the voltage waveform of alternators operating in parallel and the mains voltage waveform differs, there are superimposed currents in all three winding phases of the base wave, principally of the third order. They return through the neutral conductor. The magnitude of these currents depends on the difference in potential between the harmonic voltage and the alternators reactance.

Since this subjects the winding and neutral conductor to a thermal load, this current has to be reduced by use of a neutral conductor choke. 4.4.2 DROOP ON RESISTIVE LOADS

If the power factor is unity , as in case of resistive loads, the voltage droop available is NIL and in such cases load sharing can only be done by governor of the engine. Therefore it is essential that the speed droop should be set very accurately and response of both the governors should be identical to avoid any mis-match. Since reactive kVA is not available therefore synchronising torque available is minimum and the system is ‘inherently unstable’.


41

ALTERNATORS

SECTION 5

PROTECTION OF ALTERNATORS


42

PROTECTION OF ALTERNATORS

5.1 EXPLANATION OF TERMINOLOGY RELATED TO GENERATOR PROTECTION / CONTROL / SYNCHRONISATION The relays used for various protections are explained hereunder : OVER AND UNDER VOLTAGE PROTECTION : Over voltage protection relay protect the machine from insulation damage and over fluxing . It also protects the machine from sudden increase or decrease of voltage due to the sudden heavy load change of the machine apart from protecting the loads from abnormal voltage i.e. on low voltage the motor may heat up due to stalling. OVER AND UNDER FREQUENCY PROTECTION : Under frequency relay provides protection against overloading or governor failure and resultant stator core over-fluxing and therefore overheating due to low frequency at nominal system voltage; Under-frequency protection can also be used for shedding application. Over-frequency protection protects the machine against over- speeding due to failure of governing system or due to load throw off. OVER CURRENT AND EARTH FAULT PROTECTION : Over heating of generator may also result from overloading of generator. An IDMT relay is recommended to protect the generator due to excess load. Earth fault relay protects the generator from phase to earth fault and also from unbalance current. UNBALANCE PROTECTION : Unbalance current results in negative phase sequence current in the alternator which results in excessive heating of alternator if the unbalance / negative sequence current exceeds above 15%. Unbalance protection therefore necessary for protecting the alternator against over heating. STATOR EARTH FAULT : Stator earth fault results in zero sequence voltage and is detected by over voltage relay with very low settings along with open delta transformer. RESTRICTED EARTH FAULT: This protection allows the implementation of zero current differential protection by integrating star point current. ROTOR EARTH FAULT PROTECTION : First rotor earth fault does not damage the machine but the second rotor earth fault results in severe damage to the rotor winding due to circulating currents and hence the first rotor earth fault must be detected and cleared before the winding gets damaged.


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LOSS OF EXCITATION PROTECTION : Loss of excitation protection relay protects the generator from entering in to unstable zone of operation because of loss of excitation during parallel application. REVERSE PHASE SEQUENCE PROTECTION : Reverse phase sequence protections protects the generator from synchronisation in phase reverse condition. REVERSE POWER PROTECTION : Active and reactive reverse power protection are essential requirement of synchronisation. During synchronisation the power flow from one system to other. To protect system from excessive reverse power ; reverse power protection relays are used. Reverse power may also flow from one system to another during load balancing or due to loss of excitation or prime mover failure. CHECK SYNCHRONISING RELAY/ SYNCHRO-CHECK RELAY : Check synchronising relays are required to ensure the closing of breaker with in permissible phase angle difference during synchronisation. VOLTAGE BALANCE RELAY: Voltage balance relay is only required if auto synchronisation is required . In case of manual synchronisation this relay is not required. This relay is used to minimise the difference in voltage between two generators. FREQUENCY BALANCE RELAY : Frequency balance relay is only required if auto synchronisation is required. In case of manual synchronisation this relay is not required. This relay is used to minimise the difference in frequency between two generators. LOAD BALANCING RELAY : Load balancing relays are only required if auto load balancing is required. In case of manual balancing these relays are not required. Active load balancing relay provides pulses to the governor controller; while reactive load balancing relays provide pulses to the AVR for active and reactive load balancing respectively.

DIFFERENTIAL PROTECTION : Differential protection relay are zone protection relay and operates only for the fault with in the protected zone; differential protection protects the machine from internal fault such as inter turn fault. To avoid operation of the relay for fault outside the zone biased differential relays are recommended.


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5.2 PROTECTIONS FOR VARIOUS RATINGS AND RELAY SETTINGS Recommended relay sett ings & uses of for var ious rat ings are given below 5.2.1 FOR STAND ALONE OPERATION Protection

Upto 250kVA

250 to 750kVA

750 to 2MVA

2 to 5 MVA

SEGC Relay Type

Recommended sett ings for Tr ipping

Under voltage

Required

80%(330VAC) T ime delay : 3Sec

Over voltage Required

BU1 or MRU1 115%(477VAC)

T ime delay : 1Sec

Over current and earth fault

Not must Required IRI 1or

MRI 1

P ick up value may be set up as 100% of FLC with a t r ip t ime delay of approx. 20Secs. at 100% over load & 11Secs. At 120% over load by select ing inverse t ime character ist ic and t ime mult ipl ier 0.3 . Earth Fault may be set at 10%,t ime mult ipl ier 0.5 to provide 5 Seconds delay at 20% E/F.

Rest r icted earth fault protect ion

Not must

opt iona l Requ i red opt iona l IR I 1 -1ER

Dif ferent ial /REF set value : 7.5% -12.5%

Under Frequency

47.5Hz T ime Delay: 2Secs

Over Frequency

Not must

opt iona l Required BF 1 Or MRF2 52.5Hz

T ime Delay: 2Secs

Unbalance/ negat ive phase sequence protect ion

Not Necessary opt ional requ i red MRS1

Pick up value for negat ive sequence current may be set as 15%of FLC with a t r ip t ime delay of 65Sec at 40%over load by way of select ing inverse t ime character ist ic and t ime mult ipl ier as 400.


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Protection

Upto 250kVA

250 to 750kVA

750 to 2MVA

2 to 5 MVA

SEGC Relay Type

Recommended sett ings for Tr ipping

Stator earth fault

Not must

opt ional Required IRU1-E Voltage sett ing 40V for 415V AC open delta t ransformer

Dif ferent ial protect ion Not Necessary opt iona l requ i red

IRI1-3ER or IRD1

Dif ferent ial current can be set between 10-15% of CT secondary current .

Rotor earth fault protect ion

Not Necessary opt iona l MRR1

Insulat ion res istance value for f i rst stage(warning) can be set as 70K, with a t ime delay of 2Sec. Insulat ion res istance value for second stage (t r ip) can be set as 5K , with t ime delay of 4Sec.

5.2.2 GENERATOR CONTROL RELAYS FOR PARALLEL OPERATION Protect ion

Upto 250kVA

250 to 750kVA

750 to 2MVA

2 to 5 MVA

SEGCRelay Type

Recommended sett ings

Check Synchroniz ing Relay

Required for manual synchronizat ion

Required SY/SP Frequency dif f . 0.1-0.2 Hz, F loat ing Voltage 40-50%

Voltage balance relay

Required only for auto synchronizat ion

UN1/ PSY2

Voltage dif ference 2%(PSY2). UN1 is having automat ic t racking.

Frequency balance relay


FN2 / PSY2

Frequency dif f . +/-0.2 Hz max. (PSY2) FN2 is having automat ic t racking

Act ive load balance

Required only for auto load balancing

WLA2/ FL1

WLA2 ,2% for FL1 sett ing depends on generator rat ing.

React ive load balancing

Required only for auto load balancing

WLA2/ FL1

WLA2 ,2% for FL1 sett ing depends on generator rat ing.

Synchro check relay


SY1 / PSY2

Frequency dif f . 0.1-0.2 Hz, F loat ing Voltage 40-50%


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5.2.3 GENERATOR CONTROL RELAYS FOR ALTERNATORS RUNNING IN PARALLEL WITH EACH OTHER Protection

Upto 250kVA

250 to 750kVA

750 to 2MVA

2 to 5 MVA

SEGC Relay Type


Under Voltage

80% (330VAC for 415V system) T ime delay :3 Sec.

Over Voltage

Required BU1 or MRU1 115%(477VAC for

415V system T ime Delay : 1 Sec.

Over Current Required

IRI 1 or MRI1

Pick up value as 100% of FLC with a t r ip t ime delay of 20Sec at 110% over load and 11Sec. at 120% over load by way of select ing inverse t ime character ist ic and t ime mult ip l ier 0.3

Earth Fault Protect ion Required

IRI 1 or MRI1

Earth Fault may be set as 10% t ime mult ipl ier 0.5 to provide 5Sec. delay at 20% E/F

Act ive reverse power protect ion

Required

BP1/RW1 or MRP2 or IRP

Act ive reverse power sett ing: 5-10% of rated power T ime delay: 3Sec.

React ive reverse power protect ion

Required RW1

React ive reverse power sett ing: 5-10% of rated power T ime delay: 3Sec.

Reverse Phase Sequence

Required BV1 F ixed phase sequence sett ing

Loss of excitat ion protect ion

Required MRQ1 Sett ing depends on generator reactance

Under Frequency

47.5Hz T ime delay : 2 Sec.

Over Frequency

Required BF1 or MRF2 52.5 Hz

T ime delay : 2Sec.


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Protect ion

Upto 250kVA

250 to 750kVA

750 to 2MVA

2 to 5 MVA

SEGCRelay Type


Stator earth Fault

Opt ional Required IRU1-E

Voltage sett ing 40V for 415VAC open delta t ransformer.

Dif ferent ial protect ion

Not must

Opt ional Required

IRI1-3ER or IRD1-G

Different ial current can be set between 10-15% of CT secondary current

Unbalance Protect ion

opt ional Required MRS1

Pick up value for negat ive phase sequence current may be set as 15% of FLC ,with a t r ip t ime delay of 65.4 Sec at 40% over load by way of select ing inverse t ime character ist ic & t ime mult ipl ier 400.

Rotor earth fault protect ion

Not necessary opt ional

required MRR1

Insulat ion res istance value for f i rst stage(Warning)can be set as 70K with a t ime delay of 2Sec. Insulat ion res istance value for second stage (t r ip) can be set as 5K, with a t ime delay of 4Sec.

5.3 PROTECTION RELAY SETTINGS It is to be clearly understood that the relay settings for protection of alternator is responsibility of Gen set builder . Recommended values that are indicated here for guidelines only and not for final settings of the relay. All over current relay settings must be done considering the derated ratings of the alternator. For example when an over sized alternator is selected for reducing distortion due to D.C. drives /Variable frequency drives / non linear loads , the relay settings should not be done based on the kVA rating under standard conditions. It should be done as per current corresponding to derated kVA.


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5.4 CORELATION OF CIRCUIT BREAKER AND PROTECTION RELAYS 5.4 CORELATION OF CIRCUIT BREAKER AND PROTECTION RELAYS

Many t imes for smal l rat ings of alternators only an air ci rcuit breaker or a MCCB with i t s bui l t in protect ion system is provided. These Circuit Breakers /MCCB are avai lable in f ix rat ings such as 630/800/ 1000/1250/1600/2000 A and they are selected based on the rated current of alternator. The CB/MCCB has fol lowing bui l t in protect ion

Many t imes for smal l rat ings of alternators only an air ci rcuit breaker or a MCCB with i t s bui l t in protect ion system is provided. These Circuit Breakers /MCCB are avai lable in f ix rat ings such as 630/800/ 1000/1250/1600/2000 A and they are selected based on the rated current of alternator. The CB/MCCB has fol lowing bui l t in protect ion

I L = Long delay with adjustable pick up for current and t ime delay IL = Long delay with adjustable pick up for current and t ime delay I sc = Short delay with adjustable pick up for current and t ime delay I sc = Short delay with adjustable pick up for current and t ime delay

Instantaneous unit with adjustable pick up for current Instantaneous unit with adjustable pick up for current

Example : Example : Let us assume 380KVA alternator is provided with a CB along with its built in protection since the rated current of this alternator is 530A CB selected shall be of 630A (Nearest available rating) Max. current drawn is 475A ,Hence the pick up value of time delay should be set as 1.1 x 475 =525A and knob should be set at 0.85 IFL and time delay at 20Secs.

Let us assume 380KVA alternator is provided with a CB along with its built in protection since the rated current of this alternator is 530A CB selected shall be of 630A (Nearest available rating) Max. current drawn is 475A ,Hence the pick up value of time delay should be set as 1.1 x 475 =525A and knob should be set at 0.85 IFL and time delay at 20Secs.

The short delay can be set at 475 x 2= 950A and knob should be set at 1.5ISC with

a time delay of 5 Secs. The short delay can be set at 475 x 2= 950A and knob should be set at 1.5ISC with

a time delay of 5 Secs. Since the alternator can with stand the 300% Full Load Current for 10 Secs Hence

Instantaneous unit should be set at 530 x3 = 1650A and knob should be set at 2.5 IFL

Since the alternator can with stand the 300% Full Load Current for 10 Secs Hence Instantaneous unit should be set at 530 x3 = 1650A and knob should be set at 2.5 IFL

The above is only a illustrative example and normally these settings have The above is only a illustrative example and normally these settings have to be chosen by the “system designer” of the D.G. set supplier.


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ALTERNATORS

SECTION 6

TESTING OF ALTERNATORS


50

TESTING OF ALTERNATORS

6.1 STANDARD FACTORY TESTS

Each ‘LSC’ Alternators is subjected to following tests at factory : • Measurement of cold winding Resistance • Measurement of Insulation Resistance (in cold condition) • High Voltage Test (in cold condition) • Remanence Voltage Measurement • Phase Sequence Test • Voltage Balance at No-load • AVR Adjustments ⇒ Under speed protection adjustment ⇒ Terminal voltage adjustment ⇒ Droop potentiometer setting (for parallel operation)

• Voltage Regulation Test (with inductive load) • Heat Run Test (with inductive load for 1/2 hr.) • Measurement of Insulation Resistance (in hot condition) • High Voltage Test (in hot condition) • Checks for Optional Items (if any) 6.2 SPECIAL FACTORY TESTS

Following tests can also be conducted on alternator at EXTRA COST • Open Circuit Characteristic Test • Short Circuit Characteristic Test • Excess Current Test • Temperature Rise Test • THD Measurement • TVD Measurement • Over Speed Test • Vibration Measurement Test • Noise Level Measurement


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Documents

Technical Manual Lsc Alternators