The main types of load on a system are domestic, commercial, agricultural, industrial, and municipal, traction etc. Accordingly the consumers may be categorised as domestic consumers, commercial consumers, agricultural consumers, industrial consumers (small, medium and large), bulk consumers etc.
1. Domestic Consumers:
Residential load consists of lights, fans, and appliances such as radios, TVs, heaters, electric irons, refrigerators, electric water heaters, washing machines, coolers, air-conditioners, domestic pump sets etc. Domestic consumers are given single phase supply up to a load of 5 kW and a 3-phase supply for load exceeding 5 kW.
The small consumers generally use all the light points simultaneously so their demand factor is high (almost unity). Big domestic consumers may have demand factor low (around 0.5). During summer the major part of domestic load may consist of fan load during day and light and fan load during evenings and early mornings and some air-conditioner load.
During winter, the major load is light load during evenings and early mornings and some heater load. The tariffs applicable to domestic consumers are simple tariff, flat rate tariff or block rate tariff. In addition meter rent and electricity duty are also charged from the consumers.
2. Commercial Consumers:
Non-residential premises, such as shops, business-houses, cinemas, hotels, public offices, clubs etc. fall under this category. The load mainly consists of lights, fans and small electric appliances. The load remains fairly constant from around morning 10 to evening 9 hours. During night the load may consist of some lighting load. The demand factor is fairly high. Such consumers are given single phase supply for loads up to 5 kW and three phase supply for loads exceeding 5 kW.
Typical chronological load curve for commercial consumers is shown in Fig. 15.2. The tariffs applicable to commercial consumers are also simple tariff, flat rate tariff or block rate tariff but charges per unit are higher in comparison to those in case of domestic consumers. In addition, meter rent and electricity duty are also charged from the consumers. Sometimes there is also a provision for minimum charges in case the energy consumption remains below a certain prescribed limit.
3. Agricultural Consumers:
Consumers drawing power up to 20 kW for irrigation pumping units are categorized as agricultural consumers. Such consumers are given a three phase supply. The loads of the tube wells used for irrigation constitute a substantial portion of the system load. The demand factor and diversity factor are both almost unity. Figure 15.3 depicts the typical chronological load curve for agricultural or irrigation load.
Agricultural consumers are charged at a flat rate tariff which may be either on the basis of a fixed charge per unit consumed or a fixed charge per kW or hp of connected load.
4. Industrial Consumers:
Industrial consumers may further be categorised as small industrial consumers, medium industrial consumers and large industrial consumers according to the rating of loads.
Small industrial consumers are owners of small workshops, atta chakkis, wheat threshers, saw machines and other small manufacturing and repair shops with load not exceeding 20 kW. The demand factor depends on the nature of load but usually it is high (around 0.8). Such consumers are given 3-phase supply at 415 V. A block tariff is usually offered to such consumers.
Industrial consumers with loads exceeding 20 kW but not exceeding 100 kW fall under the category of medium industrial consumers. They are given three phase supply at 415 V and are usually charged on two part tariff.
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Industrial consumers with loads exceeding 100 kW are categorized as large industrial consumers. They are supplied power at 11 or 33 kV, and in rare cases, at 415 V three phase depending on the requirement of the consumers. The demand factor may be around 0.5. Such consumers are usually charged kVA maximum demand tariff. Typical chronological load curve for industrial load is depicted in Fig. 15.4.
5. Bulk Consumers:
Power consumers such as railways, public work departments, educational institutions, military establishments, hospitals having loads exceeding 100 kW fall under the category of bulk consumers. Bulk consumers are usually supplied by 3-phase supply at 415 V or 11 kV depending on their requirements. Such consumers are charged at flat rate.
6. Street Lighting:
Power supply given for the lighting of parks, roads and streets under the municipal committees, municipal boards or panchayats comes under this category. Supply for street lighting is given at 415 V three phases or 240 V single phases. Such a load has demand factor and diversity factor of unity.
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The switching on the lights and their switching off is synchronised with dusk and dawn respectively. Separate distributors are run for street lighting to enable their switching simultaneously. The tariff charged for street lighting is such that it recovers the cost of the energy consumed as well as the cost of replacement of lamps. Chronological load curve for street lighting is shown in Fig. 15.5.
7. Water Supply:
The load for water supply is for pumping water to the overhead tanks. It is generally possible to fit this load during system off peak hours, usually during night hours.