Electricity Billing and Power Factor Correction improvement

Murali Krishnan KAsst. Professor Dept. Of EEEAWH Engg. College

Lecture -3 Electrical system

EE09 L 09 ENERGY AUDITING, CONSERVATION

AND MANAGEMENT

05/03/2023AWH Engineering College2

Electricity Billing Cost of Electricity – Cost/kWH

Need for Electricity Billing The cost of purchasing the primary energy and

converting it to electricity; The cost of transporting electricity around a region or

country; The cost of distributing electricity to the customer;

and The cost involved in meter reading, billing and

managing customers’ accounts.


Electricity demand profile (Load Curve)


Solutions

Build more power stations and reinforce their transmission and distribution networks, which is a very costly solution;

or Discourage their customers from consuming

large amounts of electricity at times when electricity demand is high.


Electricity tariffs Some utility companies meter their customers in kW

and kWh rather than kVA and kVAh. if a utility company meters its customers in kW, then

it must levy an additional reactive power charge in kVArh.

This ensures that the utility is paid for all the power it supplies to the site, and not penalized for the customer’s poor power factor.

Types of Electricity Tariff Domestic tariffs Block electricity tariff Maximum demand tariff


Domestic electricity tariffs


Block electricity tariff


Time of day metering/Time-of-use pricing Time of Day metering (TOD), also known as Time of Usage

(TOU) or Seasonal Time of Day (SToD), metering involves dividing the day, month and year into tariff slots

Higher rates at peak load periods and low tariff rates at off-peak load periods.

While this can be used to automatically control usage on the part of the customer (resulting in automatic load control),

It is often simply the customers responsibility to control his own usage, or pay accordingly (voluntary load control).

This also allows the utilities to plan their transmission infrastructure appropriately


Maximum demand tariff


Typical Seasonal Time of Day Tariff


Problems


Solutions


Kerala Electricity Tariff Up to 40 units – Rs. 1.5 per unit 41 to 80 units – Rs. 2.2 per unit 81 to 120 units – Rs. 3 per unit 121 to 150 units – Rs. 3.80 per unit 151 to 200 units – Rs. 5.30 per unit 201 to 300 units – Rs. 6.50 per unit Up to 350 units – uniform rate of Rs. 5 per unit (no slabs, flat tariff) Up to 400 units – uniform rate of Rs. 5.5 per unit (flat tariff) Up to 500 units – uniform rate of Rs. 6 per unit (flat tariff) Above 500 units – uniform rate of Rs. 7 per unit (flat tariff)


Load management of electricity The ‘true’ cost of electricity production varies

with demand on the network, and that through the use of pricing mechanisms such as the ‘pool’ it is possible to introduce real-time electricity pricing.

The load factor for any given period represents the percentage of time for which plant and equipment operates during that period.


From the utility companies’ point of view organizations which possess a high load factor are potentially more desirable customers, since they will be buying more electrical energy for a given amount of investment in generation and distribution equipment.


Supply side and demand sideThe collective term for the operations performed by utility companies is the ‘supply side’, whereas energy consumption by customers is referred to as the ‘demand side’


supply-side measure’ since the solution lies wholly with the utility company

demand-side measure’ since the solution to the problem lies with the customer.

Through management of the ‘demand side’ in this way it is possible for utility companies to utilize their resources efficiently and thus achieve substantial cost savings


Energy demand management Energy demand management, also known as demand side

management (DSM), is the modification of consumer demand for energy through various methods such as financial incentives and education.

Usually, the goal of demand side management is to encourage the consumer to use less energy during peak hours, or to move the time of energy use to off-peak times such as nighttime and weekends.

Peak demand management does not necessarily decrease total energy consumption, but could be expected to reduce the need for investments in networks and/or power plants for meeting peak demands.

An example is the use of energy storage units to store energy during off-peak hours and discharge them during peak hour


DSM programs to encourage customers to conserve energy, and persuade as many as possible to shift their day-time load to the nighttime.

In the DSM programs include such measures as financial support for feasibility studies, free advice on techniques, capital grants towards the cost of new equipment, and even the free issue to customers of low energy light bulbs.

it more economical to persuade their customers to conserve energy, rather than be forced to build new generating plant.


For e.g..- The cost of constructing new generating capacity to be in the region of $1200–$1500/kW, which compared very poorly with the maximum of $400/kW of electricity saved


Power factor The power factor of an AC electrical power

system is defined as the ratio of the real power flowing to the load, to the apparent power in the circuit


What is PF ? Most plant loads are Inductive and require a

magnetic field to operate: Motors Transformers Florescent lighting

The magnetic field is necessary, but produces no useful work

The utility must supply the power to produce the magnetic field and the power to produce the useful work:

You pay for all of it! » These two types of current are the ACTIVE and

REACTIVE components


Similarly, motors require REACTIVE power to set up the magnetic field while the ACTIVE power produces the useful work (shaft horsepower). Total Power is the vector sum of the two & represents what you pay for:


For example, to get 1 kW of real power, if the power factor is unity, 1 kVA of apparent power needs to be transferred (1 kW ÷ 1 = 1 kVA).

At low values of power factor, more apparent power needs to be transferred to get the same real power.

To get 1 kW of real power at 0.2 power factor, 5 kVA of apparent power needs to be transferred (1 kW ÷ 0.2 = 5 kVA).


Types of loads Linear loads

Loads like (resistive, inductive, capacitive, motors) Non-linear loads

loads having power electronic equipment's E.g. Motors driven by drives



In linear circuits having only sinusoidal currents and voltages of one frequency, the power factor arises only from the difference in phase between the current and voltage.

This is "displacement power factor" In non linear circuits, the power factor

arises due non sinusoidal currents and voltages & the difference in phase between the current and voltage.

This is “Distortion Power factor & displacement power factor"


Disadvantages of low power factor Large kVA ratings of machine. Greater conductor size. Large copper losses Poor voltage regulation Reduced handling capacity of system


Power factor improvementPower factor correction of linear loads

Linear loads with low power factor (such as induction motors) can be corrected with a passive network of capacitors or inductors.

Power factor correction of nonlinear loads Non-linear loads, such as rectifiers, distort the

current drawn from the system. In such cases, active or passive power factor

correction may be used to counteract the distortion and raise the power factor.


Power factor correction of linear loads

1. Using Passive Elements :- Capacitor

1. Reactive Power Control Relay; 2. Network connection points; 3. Slow-blow Fuses; 4. Inrush Limiting Contactors; 5. Capacitors (single-phase or three-phase units, delta-connection); 6. Transformer (for controls and ventilation fans)


Merits & DemeritsAdvantages:1. Losses are low in static capacitors2. There is no moving part, therefore need low maintenance3. It can work in normal air conditions (i.e. ordinary atmospheric

conditions)4. Do not require a foundation for installation5. They are lightweight so it is can be easy to installedDisadvantages:6. The age of static capacitor bank is less (8 – 10 years)7. With changing load, we have to ON or OFF the capacitor bank,

which causes switching surges on the system8. If the rated voltage increases, then it causes damage it9. Once the capacitors spoiled, then repairing is costly



2. Synchronous Condenser An unloaded synchronous motor can supply

reactive power. The reactive power drawn by the synchronous

motor is a function of its field excitation. Whenever a Synchronous motor is over-exited

then it provides leading current and works like a capacitor.


Merits & DemeritsAdvantages:1. Long life (almost 25 years)2. High Reliability3. Step-less adjustment of power factor.4. No generation of harmonics of maintenance5. The faults can be removed easily6. It’s not affected by harmonics.7. Require Low maintenance (only periodic bearing greasing is necessary) Disadvantages: It is expensive (maintenance cost is also high) and therefore mostly used by

large power users. An auxiliary device has to be used for this operation because synchronous

motor has no self starting torque It produces noise




3. Phase advancer. Phase advancer is a simple AC exciter which is connected on the main

shaft of the motor and operates with the motor’s rotor circuit for power factor improvement.

Phase advancer is used to improve the power factor of induction motor in industries.

As the stator windings of induction motor takes lagging current 90° out of phase with Voltage, therefore the power factor of induction motor is low.

If the exciting ampere-turns are excited by external AC source, then there would be no effect of exciting current on stator windings.

Therefore the power factor of induction motor will be improved. This process is done by Phase advancer.


Advantages: The phase advancer can be easily used where the use of

synchronous motors is UnacceptableDisadvantage: Using Phase advancer is not economical for motors below

200 H.P. (about 150kW)


Passive PFC The simplest way to control the harmonic

current is to use a filter: it is possible to design a filter that passes current only at line frequency (50 or 60 Hz).

This filter reduces the harmonic current, which means that the non-linear device now looks like a linear load.

At this point the power factor can be brought to near unity, using capacitors or inductors as required.

This filter requires large-value high-current inductors, however, which are bulky and expensive.


Advantages & disadvantages of Passive PFC


Active power factor corrector An active power factor corrector (active PFC)

is a power electronic system that changes the waveshape of current drawn by a load to improve the power factor.

The purpose is to make the load circuitry that is power factor corrected appear purely resistive (apparent power equal to real power).

In this case, the voltage and current are in phase and the reactive power consumption is zero.

This enables the most efficient delivery of electrical power from the power company to the consumer.


Active PFC circuits are based on switchmode converter techniques and are designed to compensate for distortion as well as displacement on the input current waveform.

They tend to be significantly more complex than passive approaches, but this complexity is becoming more manageable with the availability of specialized control ICs for implementing active PFC.

Active PFC operates at frequencies higher than the line frequency so that compensation of both distortion and displacement can occur within the timeframe of each line frequency cycle, resulting in corrected power factors of up to 0.99.

Documents

Electricity Billing and Power Factor Correction improvement