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.

In transformer, a Sweep Frequency Response Analysis (SFRA) test will help detect ____

Frequency response analysis is the technique whereby a sinusoidal test signal is used to measure points on the frequency response of a transfer function or impedance function.
Sweep Frequency Response Analysis (SFRA) testing provides insight into the mechanical and electrical integrity of transformers.

Main Purpose of SFRA Test:
Transformer Core displacement
Winding displacement for both rotor and transformer
Broken or loosen clamp connections
Inter turn short circuit
Internal short circuit
Winding to Core Earth fault
Winding Open circuit condition

A coil having an inductance of 100 mH is magnetically coupled to another coil having an inductance of 900 mH. The coefficient of coupling between the coils is 0.45. Calculate the equivalent inductance if the two coils are connected in series opposing.

M = k√(L₁L₂)
M= 0.45√(100*900)
M = 135 mH

L_eq for opposite connection of coils = L₁ + L₂ - 2M
L_eq = 900 + 100 - 2*135
L_eq = 730 mH

Magnetic tape is not practical for applications where data must be quickly recalled because tape is a/an____.

The line currents in amperes in phases a, b and c respectively are 500 +j150, 100 – j600 and – 300 + j600 referred to the same reference vector with phase sequence of abc. Find the symmetrical component of currents.

Calculation:

Ia1 = 1/3*(Ia + a*Ib + a²*Ic)
= 500 + j150 + (- 0.5 + j*0.866)*(100 – j6000) + (-0.5 - j*0.866)*(– 300 + j600)
= (546.41 + j*156.47) A

Ia2 = 1/3*(Ia + a²*Ib + a*Ic)
= 500 + j150 + (- 0.5 - j*0.866)*(100 – j6000) + (-0.5 + j*0.866)*(– 300 + j600)
= (-146.41 - j*56.47) A

Iao = 1/3*(Ia + Ib + Ic)
= 1/3*(500 + j150 + 100 – j6000 – 300 + j600)
= (100 + j*50) A

Which one of these is not a monitoring and diagnostic test for transformer oil?

Volatility is a statistical measure of the dispersion of returns for a given security or market index.
Analysis of a mineral oil sample for volatile compounds provides an indication of whether a fault or significant degradation has occurred.