The Swartz Type 32 Reverse Current Relay can be used to monitor the current in either positive or negative conductors of D.C. distribution networks. The detector’s primary function is to monitor low reverse feeder current levels. The front panel controls have been calibrated to millivolts, allowing the detector to work with any shunt.
Tests:
The functional test of the reverse threshold is performed by a built-in calibration controller (CAL) that has variable settings between 0 and 20 mV. The test current can be measured on the meter or by using “SIG-OUT” test jacks. 0.5V in test jacks is equal to 50mV when used at the shunt. The test current is added to the current present in the shunt leads.
Digital Meter:
The meter displays a reading from 0-20mV.
Power:
If the green LED is off, either the input power has been cut or an internal 1 A fuse has blown. This LED will be off if either the input power is not on or a 1A internal fuse has blown. The output will trip the substation in either case.
Zero:
This adjustment is to compensate for minor offsets of the high voltage isolator. It should only be required when the Over current is first installed in the substation. Measure “SIG OUT” voltage with a digital voltmeter such as Fluke 8024A or equivalent. Adjust zero for .000 + .002 volts. Warm-up periods of at least five minutes are recommended for best results. The offset will vary slightly depending on the installation. For example, when the detector is bench-tested outside its enclosure, the offset can change up to 1mV.
Instant Over current Channel:
This channel will respond to “instantaneous current” levels set by the control between 0mV and 20mV. The input from the isolator has been RC filtered to suppress current spikes and noise, preventing nuisance tripping. The buffered test jack allows for highly accurate trip threshold adjustment with a digital voltage meter. A red LED will latch on to show that a trip occurred.
Setting the “Pickup Threshold”:
Connect the common lead of the digital voltmeter to “SIG Out-com.” Connect the positive lead (+) with the instant test jack. Adjust the pickup control to the desired trip level using the DVM’s 200mV range. Please note that the knob calibration is approximate (+10%). You can also use “CAL/TEST controls” to set this control. As you press the CAL/TEST button, adjust the PICKUP knob so that the LED just turns on. Reset the LED by pressing RESET.
This post was written by Justin Tidd, Director at https://www.swartzengineering.com. For nearly half a century, Swartz Engineering has been at the forefront of industry safety. They are a family-owned company specializing in power distribution for the electrical industry. Our design ensures maximum flexibility for excellent reliability and a high return on investment.
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