Question

In the figure shown below,



If both the relays $R_1$ and $R_2$ are set for 100% plug setting, the actual operating time of $R_1$ and TMS for $R_2$ respectively are:
(Assume time grading margin of 0.6s and TMS for relay 1 is 0.15)

$\begin{array}{cccc}\text{PSM}& 3.6& 6.75& 13.5\\ \text{Time in sec for}& & & \\ \text{Time Multiplier}& 6& 3.6& 2.6\end{array}$

• A. $0.39sec,TM{S}_{R2}=0.275$
• B. $0.41sec,TM{S}_{R2}=0.142$
• C. $0.32sec,TM{S}_{R2}=0.123$
• D. $0.54sec,TM{S}_{R2}=0.112$

Answer 1

The correct option is A $0.39sec,TM{S}_{R2}=0.275$

$\text{Plug setting multiplier of relay 1}$
$=\frac{2700}{1\times 1\times \frac{200}{1}}=13.5$

Operating time corresponding to 13.5 PSM is 2.6

$\text{Actual operating time of relay 1}$
$=2.6\times TMS=2.6\times 0.15=0.39sec$

$\frac{V_2}{V_1}=\frac{I_1}{I_2}$

$\frac{33}{132}=\frac{I_1}{2700}$

$I_1=675A$

$\text{PSM of relay 2}=\frac{675}{1\times 1\times \frac{100}{1}}=6.75$

Operating time corresponding to PSM 6.75 is 3.6 s.

$\text{TMS for relay 2}=\frac{0.39+0.6}{3.6}=0.275$