The Midwest RC Series
1 VA, 2 VA
The UL recognized
RC Series of Midwest donut-type transformer is available in
ratios ranging from
50:0.1 to
300:5
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):
Options for the RC Series:
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:
To add secondary turns, the X1 lead should be wound through the CT from the side opposite H1. |
To subtract secondary turns, the X1 lead should be wound through the CT from the same side as H1.
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Current Transformer Polarity
When wired as shown, the voltage on the X1 lead will be in phase with the voltage on the power lead connecting the line to the load.
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