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RC SERIES CURRENT TRANSFORMER

 

The Midwest RC Series


Features:

  • The Volt Ampere output is 1 or 2 VA.
  • Standard leads are 24" in length.
  • 600 Volt insulation is standard. A High-Voltage option is available at an additional cost.
     

Dimensions for RC Series (inches):
Dimension Drawing for RC Series

Options for the RC Series:

  • Special Lead Lengths


Installation:

CARE MUST BE TAKEN TO ENSURE THE SECONDARY LEADS ARE CONNECTED AT ALL TIMES when current is passing through the primary conductor.

Construction:

The Midwest current transformer core is made with grain oriented steel. The core is insulated and then wound with a secondary winding. The 24" leads are permanently fastened in place and the assembly is placed in a sealed case.

RC Series Ratio Modifications


The current ratio between the primary and secondary winding is defined by the following formula:

Ns x Is = Np x Ip

Where:

Ip = Primary Current
Is = Secondary Current
Np = No. of turns on the Primary Winding
Ns = No. of turns on the Secondary Winding

Example:

On a 300:5 current transformer, Is = 5 Amps when Ip = 300 Amps, number of primary turns = 1.
Ns x 5 = 300 x 1
Ns = 60

The ratio of the current transformer can be modified by altering the number of secondary turns. Forward or backwinding the secondary leads through the window of the current transformer will add or subtract secondary turns respectively.

By adding secondary turns the same primary current will result in a decrease in secondary current output. By subtracting secondary turns the same primary current will result in greater secondary output.

Example:

On a 300:5 current transformer, if a 325:5 current ratio is desired it is necessary to add five turns to the secondary winding. Ns x 5 = 325 x 1
Ns = 65

Deducting 5 secondary turns will create a transformer with a current ratio of 275:5.
Ns x 5 = 275 x 1
Ns = 55

Ratio Modifications are achieved as shown:

Ratio Modification Drawing
To add secondary turns, the X1 lead should be wound through the CT from the side opposite H1.
Ratio Modification Drawing 2
To subtract secondary turns, the X1 lead should be wound through the CT from the same side as H1.
Current Transformer Polarity

Ratio Modification Drawing 3
When wired as shown, the voltage on the white lead will be in phase with the voltage on the power lead connecting the line to the load.