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A 6 MW load with a 0.8 lagging power factor is fed by two generators connected in parallel. The initial frequency of Generator 1 is 62 Hz, and the slope of the frequency-power curve is 1 MW/Hz.

For the above situation, answer the following:

1. Determine the operating frequency of the system and how the generators share the load.
2. Calculate the idle operating frequencies to which the generators should be adjusted for equal load sharing.
3. Explain what needs to be done to increase the system frequency by 0.5 Hz.

Answer :

The load on each generator should be reduced by 0.5 MW so that the system frequency can be increased by 0.5 Hz.

The given data contains Power Factor (Pf) = 0.8, Total Load (PL) = 6 MW, Frequency of Gen 1 (F1) = 62 Hz and Slope of frequency power curve (S) = 1 MW/Hz. The calculation of the Operating Frequency of the System can be done by sharing the load equally between two generators connected in parallel. The total load on each generator can be calculated as (Total Load / Number of Generators) = (6/2) MW = 3 MW.

The frequency power curve for a single generator can be represented as: P = (F - F0) x S, where P is the power produced by the generator, F is the frequency at which the generator is operating, F0 is the frequency at no load condition and S is the slope of the frequency power curve. The above equation can be rewritten as: F = (P / S) + F0.

Given that P is 3 MW (load on each generator), S is 1 MW/Hz and F0 is 62 Hz (Frequency of Gen. 1), the operating frequency of the system can be calculated as F = (3 / 1) + 62 = 65 Hz.

For an equal sharing of load, both the generators should operate at the same frequency. The load on Generator 1 can be calculated as (65 - 62) x 1 = 3 MW, and the load on Generator 2 can be calculated as 6 - 3 = 3 MW. Therefore, the generators share the load equally.

Calculation of Idle Operating Frequency of the Generators:

To achieve equal sharing of load, both generators must have the same load at idle conditions. The load produced by the generator at idle conditions can be calculated as follows:

P = (F - F0) x S

Given that P = 1 MS (idle condition) = 1 MW/Hz, and F0 = 62 Hz, we can calculate F as follows:

1 = (F - 62) x 1 => F = 63 Hz

Hence, the generators' idle operating frequencies should be adjusted to 63 Hz so that the generators can share the load equally.

How to Increase the System Frequency by 0.5 Hz?

To increase the system frequency by 0.5 Hz, the load on the generators should be reduced by the same amount. As a result, both generators' operating frequencies will be lowered to maintain an equal load sharing.

The load reduction on each generator can be calculated using the formula:

P = (F - F0) x S

Given that P = 0.5 MS (Load reduction) = 0.5 MW/Hz, and F0 = 62 Hz, we can calculate F as follows:

0.5 = (F - 62) x 1 => F = 62.5 Hz

Therefore, the load on each generator should be reduced by 0.5 MW so that the system frequency can be increased by 0.5 Hz.

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