Automatic Restart of Essential Motors Using Micro Processor Based Relays

8/12/2019 Automatic Restart of Essential Motors Using Micro Processor Based Relays

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A Presentation On

Automatic Restart of Essential Motors UsingMicro Processor Based Relays

Presented By:- Lal Chand Poonia2010UEE108

Supervised By:-

Dr. Anil SwarnkarAssistant ProfessorDepartment of Electrical Engg .


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Contents:-

Introduction Traditional Automatic Restarting Motor-Starting Studies Automatic Restart Using a P Protective Relay Field and Simulation Verification Result Conclusion

References


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Introduction:-

In industries electrical motors for vital functions require continuousoperation, ride through, and automatic restart operation for abnormalconditions, such as momentary voltage loss, voltage dips, or other system.With large essential motors, it is either impractical or not economical toprovide an uninterruptible power source. Therefore, the next option toreduce the effects of transient interrupted service is to automatically sensethe disturbance and initiate a sequenced restart of the essential motors onthe basis of process requirements.

A customized logic algorithm that is programmed into microprocessor-based motor protection relays, eliminating additional under voltage, control,timing relays, and wiring associated with traditional schemes, is described inthis presentation.


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Voltage Disturbances

Transient voltage disturbances can be a momentary voltage dip or acomplete blackout

This temporary voltage loss can cause control relays and contactors to dropout and subsequently reclose when voltage is restored.

Uncontrollable restarts of large motors pose at least three major risks

Uncontrolled portions of processes may be restarted out of sequence. Total system voltage collapse may occur due to multiple motors startingsimultaneously.

The motor-load drive train can be damaged due to transient torques

created by out-of-synchronism reclosing of system (restored) voltage and themotor residual back electromotive force (EMF) voltage.


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Traditional ride-through and restart functionalities require under voltage

relays with control relays and discrete timers. Each motor is assigned a priority based on its requirements and has three

time settings (27TD1, TD2, and TD3). Motors in different tiers may have the same 27TD1 and TD2 settings, but

TD3 is unique for each tier TD3 depends on the priority of each motor

27TD1 is the under voltage protective relay. it provides ride-throughfunctionality and is typically set between 0.2 and 1 s.

TD 2 is an off-delay timer relay and set between 5 and 10 s.

TD 3 is an on-delay timer relay that works in combination with TD2 toallow the reclosing of a motor circuit breaker once TD3 times out and ifvoltage recovers before TD 2 times out.CR 1 and CR 2 are control relays

Traditional Automatic Restarting Method


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Dynamic-motor starting studies To calculate the voltage, current, motor slip, and starting times while

starting a motor under loaded conditions. Starting a motor may cause disturbances to other loads operating on thebus to which the motor is connected. Starting large motors may cause a

serious voltage dip on the buses, causing other motors to slow down . The motor terminal voltage must be maintained at 80% of the nominalvoltage for proper motor operation.

Depending on the process, motors are prioritized for restart from 1 to 7,with 1 being the highest priority and 7 being the lowest priority.

Two different operating scenarios were considered when performing themotor-starting study

Scenario 1 was a normal configuration (intact system)

Scenario 2 was a single feed


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A partial one-line diagram


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It was deduced in Scenario 1, Starting all the Priority 1 motors togetherdid not cause a considerable voltage drop, so the Priority 2 motors wereable to be started 5 s later.

So all the motors grouped by the seven priorities will return to servicewithin 1 min after the system voltage has been restored.

in Scenario 2, starting all the Priority 1 motors simultaneously causesconsiderable voltage drop on the buses (SG-B-1 and SG-A-2), primarily dueto the starting of large motors (4,000 kW).

By alternating the motor restarts, Priority 2 motors were able to bestarted 5 s after starting the first Priority 1 motor.

It was concluded that the Priority 1 motors must be reaccelerated byalternating the motor restart between the two sections of switchgear.

The priority start timer (PST) defines when the motor has to be restartedand is set to (P: 5) s


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Table 1.Summary of selected motor restart study timing


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Automatic Restart Using a P Protective RelayThese relays have built-in voltage detection and can be used to sense thevoltage dips and trip the motor in an under voltage condition . After anunder voltage trip, the relays can restart.

Under voltage protection for motors should perform two main protectionfunctions:

It should provide backup to the current actuated overload relays fortransient under voltage conditions

It should provide protection to the motor from sustained system undervoltage conditions, which are not severe enough to cause overloadcurrents for a 49 trip, but over time can thermally degrade the statorinsulation systems. The P relay has two under voltage relay elements, 27P1 and 27P2.

27P1 is configured for a conservative value of 65% of the motor-ratedvoltage and a 0.2-s delay. 27P2 is configured for 92% of rated voltage with a 20-s delay . The 27P2

delay was set longer than the longest motor start time to preventinconvinence tripping and allow successful motor restarts.


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OUT101 is used for a protective trip for abnormal and fault conditions.OUT302 is used for an under voltage trip, and OUT304 is used for automaticrestart.

A schematic diagram for restarting using a P protective relay.


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Output OUT304:= START is controlled by the START digital bit.

STREQ asserts only when an automatic motor restart is initiated.The function of latch LT01 is to enable or disable the automatic restartfunction of the motor in the P relay.

Latch LT02 is used to determine that the motor is in running condition ornot. The STARTING digital bit asserts when the motor is starting, and theRUNNING digital bit asserts when the motor is running.

The latch bit LT03 is the ride-through timer latch that starts on the undervoltage trip condition. SV06PU defines a time window of 5 s.

The 27P1T digital bit is the definite-time-delayed under voltage element

that triggers the automatic restart.The 27P2 digital bit is used to determine if the voltage has recovered.

Automatic Restart Logic


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Continued...........

The logic diagram for an automatic restart


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Continued......

When the voltage drops to the 27P1 setting and remains below 27P1 for atleast 27P1D seconds, the motor trips via output OUT302 and timer SV07

(PST) is started. If the voltage does not return before the SV06PU (outagetime) timer expires, then the system resets and no restart is performed.

If the voltage returns to above 27P2 before SV06PU (5 s) expires, then theSV07PU (PST) timer is allowed to time out, initiating an automatic restart.The voltage must return to above the 27P2 setting (92%) within 5 s beforethe P relay allows a restart.

Every motor can be set with the same or different duration timers, asneeded. In general, the PST is set with SV07T, so any automatic restarttime delay is possible. Along with these latch conditions (LT01, LT02, and

SV07T), the automatic restart part of the STREQ digital bit is supervised bythe trip and under voltage alarm 27P2 .


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3/2/2014 Automatic Restart Logic Flow Chart

Logic Flow Chart


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Field and Simulation Verification Result This automatic restart logic was implemented in P protective relays and

tested in the field successfully. The automatic restart function of the motoris enabled via the pushbutton on the relay front panel. The motor isrunning during the initiation of the under voltage trip. The voltage isreduced 0.2 s andbrought back to >92% of nominal voltage within the 5 s OUT304 assertion,initiating an automatic restart of the motor. Results shows in table below


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Conclusion Use of this scheme in the motor protection system allows for recording or

logging of motor-restart events, oscillograph data, and conditions.

The use of a P relay that provides motor protection reduces wiringcomplexity.A P relay also has built-in voltage detection capability thathelps reduce cost and to trip the motor and restart again.

Dynamic-motor-starting studies can be performed to ensure a stablesystem when motors are restarted. Motor-restart studies help in

determining the priority starting times and effects of out of sequencerestart.

This algorithm can be customized for virtually any motor or loadcombination, with motor restart priority being customized by the user.Motors will be restarted according to their priorities in predefined time

(like 1 minute in this case) so chances of voltage loss will be neglected. There was no need for any additional control circuitry, but additional

controls from supervisory control and data acquisition or other remoteprocess controls can be accommodated in the future.


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References1) Rekha T. Jagaduri, Dennis Bradely,Larry Kingrey and Tuyen p. Nguyen,Automatic

Restart OF Essential Motors, IEEE Ind. App., pp. 1077 -2618, Apr 2013.2) V. Popescu and L. Oprea, Optimized reacceleration of the motor load in a large

industrial power system, in Proc. 12th IEEE Mediterranean Electrotechnical Conf.,May 2004, pp. 947 950.

3) M. H. J. Bollen, The influence of motor reacceleration on voltage sags, IEEETrans. Ind. Appl., vol. 31, no. 4, pp. 667 674, July/Aug. 1995.

4) R. A. Hanna, P. Bulmer, and R. Kohistani, Minimizing refinery upset during power

interruptions using PLC control, in Proc. 39th Annual Petroleum ChemicalIndustry Conf., San Antonio, TX, Sept. 1992, pp. 185 195.5) J. J. Novak and R. D. Kirby, Better, faster, and more economical integrated

protective relaying and control using digital bits and logic, IEEE Trans. Ind. Appl.,vol. 46, no. 4, pp. 1281 1294, July/Aug. 2010.

6) IEEE Graphic Symbols for Electrical and Electronics Diagrams, IEEE Standard 315-1975.

7) IEEE Guide for AC Motor Protection, IEEE Standard C37.96-2000.8) Motors and Generators, ANSI/NEMA Standard MG 1-2003.

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Automatic Restart of Essential Motors Using Micro Processor Based Relays