Types of Electrical Tariffs (LT and HT)
Types of Tariffs :
(a) Simple rate tariff
(b) Block rate tariff
(c) Two part tariff
(d) Maximum demand tariff
(e) Power factor tariff
(f) Three part tariff.
(g) (i) Time-off day tariff, (ii) Peak-off day tariff
(h) Load factor tariff
(i) Availability Base Tariff (ABT).
Study of these tariffs :
There are many forms of charging a consumer, but the following are the general methods which are commonly used :
(a) Simple flat rate tariff
(b) Block rate tariff
(c) Two part tariff
(d) Maximum demand tariff
(e) Power factor tariff
(f) Three part tariff
(a) Flat rate tariff :
- This is the simple way of charging a consumer. In this form the consumer is charged a energy bill equal to energy charges per unit multiplied by the total number of units consumed by the consumer.
- The form of tariff may be applied at different rates to the domestic light and fan consumer and the power.
- The main disadvantage of this form of tariff is that if a consumer does not uses any energy during a certain period he will not be charged though the plant has some installed capacity reserved for him.
(b) Block rate tariff :
- This type of tariff uses a method of charging a consumer in blocks. Generally, block of first few units is charged at high rate, then next block of some units is charged at low rate and a third block of remaining units consumed by him is charged at still reduced rate.
- In Maharashtra, the electricity board uses this type of tort but in the reverse manner so as to reduce the consumption of electricity for light and tan loads. It charges less for the first block and the rate increases toe the succeeding blocks.
- The example may be as follows : Suppose that a consumer uses 100 units. He may be charged at ₹ 3/- per unit for first 20 units, at ₹2/- per unit for next 30 units and at ₹ 150 for the remaining
- The advantage of this type of tariff is that the consumer is charged at low rate it he uses more electricity which will increase the load factor of the system and hence cost of generation is reduced.
- The disadvantage is that it does not take into account the M.D. of the consumer.
(c) Two part tariff :
- In the two part tariff, the consumer has to pay his electricity bill , which consists of two parts, one part being energy charges depending upon the maximum demand of the consumer and the other part consists of energy charges on the actual energy consumed by him.
- Mathematically, Total charges = A x kW + B x kWh.
- The charges of kW M.D. and kWh consumed may be flat rate type or it can be block rate type. This system need a M.D. indicator to be installed at the premises of the consumer, hence such type of tariff will be suitable to large and medium scale industries
- When M.D. is not installed some arbitrary method is used to determine M.D. of the consumer from its connected load and the billing is charged as per the calculated M.D.
(d) Maximum demand tariff :
- It is similar to two part tariff energy charges are computed on the basis of M.D. of the consumer and the actual energy consumed by the consumer.
- In this type of tariff, a M.D. indicator is installed at the premises of the consumer and no arbitory means are used to compute the M.D.
- This type of tariff is used for big industries. It is not suitable for small consumers and domestic light and fan connections, as the cost of M.D. indicator for such consumers will be too high in comparison to energy bill which they have to pay.
(e) Power factor tariff :
- Low p.f. of the consumer needs high current, increased capacity of plant low efficiency of machines and equipments etc. Hence, it is necessary that the consumer be made to use electricity at high power factor otherwise he should be charged more.
- This makes the supply agency to frame a p.f. based tariff.
Following are the types of p.f. tariff :
(i) KVA maximum demand tariff
(ii) Sliding scale tariff
(iii) kWh and KVAR tariff
(i) KVA maximum demand tariff :
This type of tariff is a modification of two part tariff. The part consist of energy charged depending upon the KVA maximum demand of the consumer. For reducing KVA maximum demand, the consumer will use machines and equipments at high p.f. or will use the pf improving system. The other part will consists of energy charges based upon the actual energy consumed by the consumer. In this case, also a block rate can be applicable.
(ii) Sliding scale tariff :
In this type of tariff, a datum value of the p.f. is fixed by the supply agency and a consumer is charged at certain rate when he uses energy of this pf but if the p.f. of the consumer is less than above specified value he is penalized, at the same time if he operates at higher power factor than specified, he is given certain discount in the energy bill.
(iii) kWh and KVAR tariff :
It is similar to KVA maximum demand tariff. In this type, the consumer is charged on the basis of KVAR and actual energy consumption. If p.f. is low the KVAR will be high, hence he will be required to pay more
(iv) Three part tariff :
This type of tariff is a modification of two part tariff. It consists of three components for billing a consumer i.e. a fixed charge, semi-fixed charge and running charge.
Mathematically, Energy bill = ₹ (A + B x kW + C x kWh)
Where,
A = Fixed charge, consisting of interest and depreciation on the cost of distribution of energy and labour cost of official staff for collecting bills etc.
B = Charge per kW of M.D.
C = Charge per kWh of energy consumed.
This type of tariff is applied to very big consumers
(g) (i) Time-off-day tariff :
- The time-off-day tariff makes use of Time of Usage (TOU) metering, which involves dividing the day, month and year into tariff slots.
- Then higher rates are applied for using energy at peak load periods and low tariff rates are applied for using energy at off -peak load periods.
- By this way the consumer tries to reduce his load demand at peak hours to reduce his energy bills, the effect is the load on the station is reduced, reducing peak load, which helps in planning of transmission, distribution and other infrastructure of power supply system.
- For this purpose domestic variable rate meters can be used, which permit two tariffs i.e. peak tariff and off peak tariff. In such installations, a simple electro mechanical time switch may be used.
(ii) Peak-off-day tariff :
- In this type of tariff, consumers are offered electricity during peak-off period of the day, so that generating plants working at low loads can be made to work at high loads, reducing the cost of generation.
- Consumers using energy during off peak loads can be charged at low rates.
- In such cases, a timer switch with energy-meter can be provided which will cut-off supply to consumer during peak hours of the day.
(h) Load factor tariff :
Load factor = Average load/Maximum demand
Maximum consumption possible = Contract demand kVA x Actual p.f. x Total number of hours in a month Load factor of domestic consumer = 0.5.
Load factor of commercial consumer and industrial consumer = 0.5 +0.8
This will encourage the consumer to improve power factor