Question 1:
Following transformer testing on a 100 kVA, 50 Hz, 1000 V:250 V step-down transformer, the following results table was compiled:
|
|
Open-circuit test
|
Short-circuit test
|
|
Voltmeter reading (V)
|
1000
|
505
|
|
Ammeter reading (A)
|
2.5
|
7.2
|
|
Wattmeter reading (W)
|
105
|
88
|
a) From the transformer data and table determine the transformer's equivalent resistive parameters.
b) Likewise, determine the transformer's equivalent inductive parameters.
The transformer of (a) and (b) has an iron loss of 92 W and it is used on full-load with a power factor of one. What are the copper losses
Question 2:
An industrial unit utilising electrical machinery has a maximum demand of 250 kW, it has a power factor of 0.8 and a load factor of 0.35.
Consider the following tariffs, and determine their annual (consider I year having 365 days) cost of electricity and their corresponding costing per kWh:
A maximum demand charge of £25/kW and a running charge of 5 p/kWh.
A maximum demand charge of £20/kVA and a running charge of 5 p/kWh.
A basic maximum demand charge if £25/kW. This increases by a factor of 0.15 for each 0.1 the power factor is worse than 0.9. The running charge is 5 p/kWh.