Tutorial 1

Review Questions

1.1 Explain the utilisation of electricity energy in the following fields:

a) Agricultural
b) Commercial
c) Industrial
d) Residential

1.2 Describe the major differences between American and European distribution systems in
terms of cost, flexibility, safety, and reliability.

1.3 State and explain the functions of each substation (4 levels) found in the primary
distribution system.

1.4 Give the definitions of the following terms:

a) Domestic consumer
b) Commercial consumer
c) Industrial consumer
d) Kilowatts of maximum demand
e) Average power factor
f) Peak period and Off-Peak period

1.5 Express the following terms with brief descriptions:

a) Maximum demand
b) Load factor
c) Diversity factor
d) Tariffs

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Questions

1.1 A generating station has a maximum demand of 35,500 kW and has a connected load of
65,000 kW. The number of units annually generated is 2.56 x 10 8 kWh. Calculate the
demand factor and the load factor. [Ans. 0.45; 0.823]

1.2 A domestic lighting installation having fifteen 12 watts LED lamps is operated as follows:
5 lamps from 6pm until 8pm
10 lamps from 8pm until 10pm
6 lamps from 10pm until 12am

(a) Determine the connected load, the maximum demand, the demand factor, and the
daily load factor [Ans. 180 W, 120 W, 46.7%, 17.5%]
(b) Also determine the improved load factor if a 2 kW immersion heater is used from
1pm until 5pm and a 2 kW vacuum from 8pm until 11pm [Ans. 28.5%]

1.3 A power generation station supplies the following loads to various consumers: 15,000 kW,
12,000 kW, 8,500 kW, 6,000 kW and 450 kW. The station has a maximum demand of
22,000 kW. The annual load factor of the station is 0.48. Calculate:
(a) the number of units supplied annually
(b) the demand factor
(c) the diversity factor
[Ans. (a) 9.25 x 107 units, (b) 0.252 and (c) 1.907]

1.4 There are four consumers of electricity having different load requirements at different
times as follows:

Consumer Maximum Demand Load Demand Others

1 2 kW at 9pm 1.6 kW at 8pm Load factor = 15%
2 2 kW at 12 noon 1 kW at 8pm Average load = 500 W
3 8 kW at 5pm 5 kW at 8pm Load Factor = 25%
4 4 kW at 8pm - Average load = 1 kW

Determine:
(a) the diversity factor [Ans. 1.379]
(b) the load factor and average load of each consumer [Ans. Consumer 1: 0.3 kW, 15%;
Consumer 2: 0.5 kW, 25%; Consumer 3: 2 kW, 25%; Consumer 4: 1 kW, 25%]
(c) the average load and load factor of the combined load [Ans. 3.8 kW, 32.76%]

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1.5 A factory has its monthly (take 30 days) electric power consumptions as follows:

No. Electric Equipment/Appliances Rating/ Operating Period Per Day

1. Pump motors 2 X 25 HP, 0.78 PF lagging/ 5 hours
2. Conveyer motors 8 X 2.5 kVA, 0.82 PF lagging/ 18 hours
3. Heating elements 5 X 3 kW/ 8 hours
4. Air Conditionings 20 X 5 HP, 0.86 PF lagging/ 18 hours
5. Lighting 7 kVA, 0.95 PF lagging/ 20 hours
6. Others 45 kVA, 0.90 PF lagging/ 20 hours

The tariff rate (Tariff E1 – TNB) is as follows:

Tariff E1 (Medium Voltage General Industrial Tariff) Unit Rates

For each kilowatt of maximum demand per month RM/kW 19.50
For all kWh Sen/kWh 22.2

Calculate:
(a) The total monthly energy consumption (in kWh and kVArh) of the factory [Ans.
86625 kWh + j47654 kVArh]
(b) The maximum demand for this factory if the load factor is considered as 72% [Ans.
167.1 kW]
(c) Average power factor and the total monthly bill charge [Ans. 0.88, RM22,487.25]

1.6 A load profiling data has been extracted from a distribution area consisting of 3 groups of
individual consumers. Table 1-1 depicts the 10 days average energy consumption (in kVA)
for those individual consumers.

Table 1-1
Individual
1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th
Group
1 42 53 126 34 65 76 90 23 55 80
2 256 128 112 89 134 178 136 184 105 160
3 89 78 63 77 95 72 69 167 111 125

Calculate the diversity factor for the distribution area. What is the nearest standard size of
the distribution transformer that serving the distribution area? [Ans. 1.42, 400 kVA]

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1.7 An agriculture product of 1000 kg is raised through a vertical distance of 12m in 15 s by a
hoist. The efficiency of the hoist gearing is 30% and that of the driving motor is 80%. If the
hoist system is operates 18 hours/ day with the maximum demand of 42.3 kW, determine:
(a) The electrical power input to the motor [Ans. 32.7 kW]
(b) The monthly load factor (take 1 month = 30 days) [Ans. 0.58]
(c) Total monthly bill charge due to the motor utilisation (take RM0.23/ kWh) [Ans.
RM4,061.34]

1.8 A 100 MW power station delivers 100 MW for 2 hours, 50 MW for 6 hours and is shut
down for the rest of each day. It is also shut down for maintenance for 45 days each year
Calculate its annual load factor. [Ans. 20.8%]

1.9 A diesel station supplies the following loads to various consumers:

Industrial consumer = 1500 kW Commercial establishment = 750 kW

Domestic power = 100 kW Domestic light = 450 kW

If the maximum demand on the station is 2500 kW and the number of kWh generated per
year is 45 x 105, determine
(a) the diversity factor
(b) annual load factor
[Ans. (a) 1.12, (b) 20.5%]

1.10 A power supply is having the following loads:

Type of load Max. demand (kW) Diversity of group Demand factor

Domestic 1500 1.2 0.8
Commercial 2000 1.1 0.9
Industrial 10000 1.25 1.0

If the overall system diversity factor is 1.35, determine (i) the maximum demand and (ii)
connected load of each type. [Ans. (i) 10,000 kW, (ii) Connected domestic load = 2250 kW,
Connected commercial load = = 2444 kW, Connected industrial load = 12500 kW]

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1.11 It has been desired to install a diesel power station to supply power in a sub-urban area
having the following particulars:

(i) 1000 houses with average connected load of 1.5 kW in each house. The demand
factor and diversity factor being 0.4 and 2.5 respectively
(ii) 10 factories having overall maximum demand of 90 kW
(iii) 7 tubewells of 7 kW each and operating together in the morning

The diversity factor among above three types of consumers is 1.2. What should be the
minimum capacity of power station? [Ans. 316 kW]

1.12 The daily demands of three consumers connected to a station are given below:

Time Consumer 1 Consumer 2 Consumer 3

12 midnight to 8 A.M. No load 200 W No load
8 A.M. to 2 P.M. 600 W No load 200 W
2 P.M. to 4 P.M. 200 W 1000 W 1200 W
4 P.M. to 10 P.M. 800 W No load No load
10 P.M. to 12 midnight No load 200 W 200 W

Plot the load curve and find (i) maximum demand of individual consumer, (ii) load factor
of individual consumer, (iii) diversity factor and (iv) the station load factor. [Ans. (i) 800 W,
1000 W, 1200 W, (ii) 45.8%, 16.7%, 13.8%, (iii) 1.25, (iv) 29.1%]

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