In a power network, 400 kV is recorded at a 415 kV bus. A 50 MVAR, 415 kV shunt reactor is connected to the bus. What is the reactive power absorbed by the shunt reactor?

The capacity of reactor = 50 MVAr when it is operated at 415 kV.
Impedance of reactor = V2/MVAr = (415*415)2/50 = 3444.5 Ω
For 400 kV,
Reactive power observed = (400*400)/3444.5
= 46.45 MVAR

Or

VAr capacity of capacitor or reactor is proportional to V²

Find the word which is correctly spelt from the given options.

The miniature circuit breaker (MCB) with Class D trip characteristics trips instantaneously when the current flowing through it reaches ____ the rated current.

Class B trip curve :
The MCB with class B trip characteristics trips instantaneously when the current flowing through it reaches between 3 to 5 times rated current. These MCBs are suitable for cable protection.

Class C trip curve:
MCB with class C trip characteristics trips instantaneously when the current flowing through it reaches between 5 to 10 times the rated current. Suitable Domestic and residential applications and electromagnetic starting loads with medium starting currents.

Class D trip curve:
MCB with class D trip characteristics trips instantaneously when the current flowing through it reaches between Above 10 (excluding 10) to 20 times the rated current. Suitable for inductive and motor loads with high starting currents.

Class K trip curve:
MCB with class K trip characteristics trips instantaneously when the current flowing through it reaches between 8 to 12 times the rated current. Suitable for inductive and motor loads with high inrush currents.

A 3-phase motor load has a p.f. of 0.397 lagging. The two wattmeter method used to measure power show the input as 30 kW. Find the reading on each wattmeter.

Here,
Cosφ = 0.397
P = 30 kW = √3*V_L*I_L*cosφ
V_L*I_L = 30kW/(√3*0.397) = 43628.48 VA

Readings of wattmeter W1 = V_L*I_L*cos(30+φ)

Readings of wattmeter W2 = V_L*I_L*cos(30-φ)

Consider the following statements associated with Buchholz's relays.
Statement 1: Buchholz's relay is a current operated device.
Statement 2 : Buchholz's relay is placed between the transformer tank and the conservator.

Buchholz relay is gas operated relay.
It will operate when internal fault occurs in transformer.
It is placed between tank to main conservator.
It has two contacts trip and alarm.
Use of Buchholz relay in distribution transformer is not economical.

The expression for voltage regulation of a short transmission line for leading power factor is given by: ____, where, 'I' is the line current, 'V_r' is the receiving end voltage, 'R' is the line resitance and 'X' is the line reactance.

For lagging power factor = (IR*cosφ + IXsinφ)/V_r
For leading power factor = (IR*cosφ - IXsinφ)/V_r
Zero voltage regulation occurs on leading power factor only.