Plug Setting Multiplier & Time Setting Multiplier

Plug Setting Multiplier & Time setting Multiplier Calculation:

Plug setting multiplier is nothing but a ratio between the actual fault current in the relay operating coil to pick up current (the relay current setting).

Plug setting multiplier Time setting multiplier

Relay pick up current= %current setting * CT ratio

Plug setting multiplier Time setting multiplier

In other words, the ratio between the CT (current transformer) secondary current to relay operating current is called plug setting multiplier (PSM).

Plug setting multiplier Time setting multiplier

Significance of Plug setting Multiplier:

In electromagnetic relay, the current setting can be done by adding resistance value. These action is performed by inserting plugs. The resistances are connected in series with the relay operating coil. The plug is a small short link which connects the relay operating coils and resistance. The high number of plug position increase the resistance value, therefore to operate the relay coils which need high value of current to energize. At that same time, the Lower number of plug position would be of less resistance, hence to operate relay coil, which needs low current value. Therefore, The plug position ensures the current setting value of the relay. Plug setting multiplier (PSM) Indicates the severity of the fault. The plus setting multiplier is used only in Electromagnetic relays not in numerical relays.

Example: If the plug position 5 means the relay operates when the fault current is 5 times of the CT ratio. i.e The supply CT is rated 400:5A and the fault current is 3200A means, the plug positon is 5 then the relay operates, because of the relay gets the current value of 25 Amps.

The operating Times is depending upon the PSM. The high value of PSM indicates the low operating time. Refer the table below.. The psm Value is normally available in the relay itself.

PSM 1.5 2.5 3 5 8 10.5
Time in sec 10 8 5 3 2 1


Time Setting Multiplier (TSM):

Plug setting multiplier Time setting multiplier relay
Plug setting multiplier Time setting multiplier relay

The time setting multiplier is used to adjust or speed up the dial setting. The dial is nothing but a rotating disc, which rotates when the fault current in the relay coil reaches the pickup current. The TMS setting value will be in percentage %. Typically, 10%, 20 %, 30 % …100% like that.

The total relay operating time= PSM time* TMS

Take an example of above mentioned, in this, consider relay TMS is 10% and PSM=8.. see the timing for PSM 8, Time =2 sec…then the relay operating time is 2 * 10% = 0.02sec.

Also see:


Please enter your comment!
Please enter your name here