### Power System Performance - Short answer questions from AMIE Exams (Winter 2022)

Answer the following in brief (2 marks each):

### Differentiate between a protective relay and a fuse.

Relay switches current flow on and off when energized/de energized. A fuse lets current flow until it reaches a pre designed limit.

### What is restructure power system?

Power restructuring, a systematic running of modifying the rules and instructions that control the power market to impart consumers for the option of power producing, those are may be traders and allowing rivalry within the traders. Deregulation improves the stock rate and usage.

### What is Static frequency drop?

It is given as

Δf0 = -M/[D + (1/R)] Hz
R = regulation
D = frequency dependency

### List the various sources of reactive power.

Some of the static sources for the reactive power in the power system are:

•     Shunt capacitors.
•     Filter banks.
•     Underground cables.
•     Transmission lines when lightly loaded.
•     Fuel cells.
•     PV systems.

### What do you understand by Sparsity?

A matrix is characterized as sparse, whenever a significant percentage of it's elements are equal to zero. The admittance or Y matrix of a power system is relatively sparse, whereas the Z of impedance matrix of the same system is proportionately full, i.e. very few zero elements.

Ybus is a Sparse Matrix that is most of elements are zero and hence less memory is required for storage.

### Where Impedance relays. Reactance relays and Mho relays ate employed?

The Impedance relay is suitable for the phase faults relaying for the lines of moderate lengths. Reactance type relays are employed for the ground faults while Mho type of relays are best suited for the long transmission lines and particularly where synchronizing power surge may occur.

### What do you understand by dead spot?

The section of Power System which is not covered under any zone of protection is called Dead Zone or Blind Zone and special kind of protection shall be provided to take care of fault in Dead Zone.

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