Electricity Tariffs for Voltage-dependent Loads

Transcription

1 Electricity Tariffs for Voltage-dependent Loads Authors: Prof C. S. Indulkar and Dr K. Ramalingam Presenter : Dr K. Ramalingam

2 Abstract These days the regulators specify that the tariff report should include: The distribution and transmission tariffs charged by the supply companies; The tariff principles adopted in framing the structures and level of the tariffs; The basis on which the appropriate breakdown is determined between fixed and variable charges; The rationale for the introduction of new and the withdrawal of old tariffs; and The methodology adopted for allocating transmissionrelated costs to customers through its transmission tariffs.

3 Supply companies usually adopt the following \ tariff structures: General Purpose single rate tariff applicable for all times of the day with a fixed charge, for customers that consume small amounts of electricity, such as residential customers and farms; Time of Use two- rate tariff applicable to peak and offpeak periods with a standing charge,applicable to Residential and Small Business customers; Time of Use Demand two- rate tariff applicable to peak and off-peak periods, a demand charge (Rs/kW ) and a fixed charge.- for Large Business and Small Business customers

4 Factors influencing the energy structure are the time of the day, the power factor, and the fuel price.. In present times, because of all-pervading computerization in electricity billing, privatization, and availability of distribution companies consumer can choose the supply company Different tariffs are essential so that each consumer should pay a fair share of the costs. Different types of load should have different forms of tariff. The bulk tariff for supplies at 132, 220 or 400 kv comprises a fixed charge to cover peak and base load charges, and appropriate running charges for peak load and other periods.

5 There are still unsolved questions with regard to electricity billing at different voltage levels. There is a need to ascertain the relative benefits and economic gains from the utility company perspective as well as from the consumer s viewpoint in the billing charges considering a range of, say, + 10%. It is necessary to know the effects of constant power loads, constant current loads, constant impedance loads and mixed loads on the billing charges. The supply company may want to increase its profits by increasing the voltage level. on-line determination of load voltages would be possible along with on-line remote metering at load centres. Knowing that the frequency based tariff is already under implementation, the paper suggests, for the first time, a tariff based on the type of voltage dependent loads.

6 This paper shows a method of determining tariffs for voltage-dependent loads. Consumers gain if the supply company uses voltage-dependent tariffs for voltage dependent loads. For mixed type of loads, the supply Company gains, if it uses voltagedependent tariffs.

7 Voltage-dependent loads The following voltage-sensitive real power characteristics are considered: P=P 0 (Vr/V 0 ) m (1) where m = 0 for constant power load, = 1 for constant current load, = 2 for constant impedance load. A mixed load of the following combination of the above three types of load is also considered for framing the tariff. P = P 0 [ (Vr/V 0 ) +0.2(Vr/V 0 ) 2 ] (2)

8 A typical composition of a substation load is as follows: Induction motors, 50-70% Synchronous motors, 10 % Lighting and Heating, 20-25% Transmission loss, 10-12%. The lighting load consumes no reactive power. The power consumed by the lighting load does not vary as the (voltage) 2, but approximately as (voltage) 1.6. The heating load maintains constant resistance with voltage and hence the power varies with (voltage) 2.

9 Statistical Analysis of Voltage-dependent Loads on Monthly Billing A consumer with a constant current load of 10 kw when the supply voltage is 400V (L-L) is considered. The supply voltage and the hours of use are statistical quantities with normal distributions. Table 1 gives mean values and standard deviations of supply voltage and daily hours of use under peak loading conditions.

10 In table 1, the mean values of voltage and daily hours of use are set equal to their nominal values. The standard deviation, σ is σ= (α /100).µ/3 (3) where α = percent variation from the mean value µ = mean value. Formula (3) signifies that the per unit deviation of a statistical quantity from its mean value is equal to its 3σ value.

11 Table 2 gives the monthly charge for a constant current load of 10 kw at 400 V (L-L) nominal voltage and at 8 hours nominal use of electricity at a constant tariff of Rs 4.4 per kw-h. A random number generator generates thirty normally distributed values of Vr and h for thirty days in a month, using the mean and standard deviations given in Table 1. Table 2 gives the values of Pr for Pr= P 0 (Vr / V 0 ) 2, where P 0 = 10 kw at the nominal voltage, V 0 = 400 V. The daily charges are equal to kw-hrs multiplied by the tariff.

12 In Table 2, the voltage and the daily usage hours vary every day in a statistical manner, and the tariff remains constant at Rs 4.4/kW-hr. Next, the tariff varys with the voltage. A tariff of Rs. T 0 /kw-hr at nominal voltage, V 0, varies with voltage Vr. If the voltage Vr exceeds the nominal voltage V 0, then the new tariff T 1 is: T 1 = T 0 (V 0 /Vr). (4) If Vr is less than V 0, then the new tariff T 2 is: T 2 = T 0 (Vr/V 0). (5)

13 Table 3 gives the results of the new study. The voltages Vr of Table 2 appear in a decreasing order of magnitude, along with the associated values of hours and Pr. The tariff at nominal voltage is Rs 4.4/kW-hr. At other voltages, the tariff suggested by formulae (4) and (5) is used. These formulae adjust the tariff by about 10 P for a 10V deviation from the nominal voltage of 400V.

14 The paper considers the constant power, constant impedance, and mixed loads. Table 4 gives the results for the different types of load indicating the monthly bills with fixed tariff and voltage dependent tariff. The study shows that the consumers gain if the supply companies use the voltagedependent tariffs for constant power, constant current, and constant impedance loads. The supply company gains for a mixed load if it uses the voltage dependent tariff.

15 Conclusions This paper suggests a voltage-dependent tariff for use by the supply companies. The tariff could be an additional principle adopted by the State Electricity Regulatory Commissions while framing the structures and level of the tariffs. Further work on electricity pricing may include voltage dependency of the reactive power in addition to the voltage dependency of the real power as presented in this paper. Future work can be on Changes in the hourly tariff dependent on the changes in the real and reactive powers, and the frequency, using appropriate weighting factors.