Group SD0627
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SEL Group
Group Members:
- Trenton Schwahn
- Brian Fettig
- Jonah Peterson
Advisor
- Dr. Rajesh Kavasseri
Project Description
Introduction: Our project’s goal is to build a test bench for a digital protective relay. The bench will simulate faults to the relay. The exact relay which we will test is an SEL 351S-7 model. This model of relay is built to protect many different bus feeders. The test bench we build will have to drive the relay’s potential and current transformer inputs with a nominal voltage of 110 volts and a nominal current of 5 amps.
Options Considered
This test bench will need to be portable and supplied from a 110VAC single phase supply per Ulteig’s request. The first and most important part of the bench will be the voltage and current injection circuits, which will need to be adjustable.
For the voltage source, a variable transformer was chosen as the most appropriate device to use. The nominal voltage of the potential inputs on the relay are at the same level as our source, so a small ratio step up transformer would be required anyways. An alternative would be to use a step up transformer and control the voltage with a divider circuit which uses a potentiometer. In either case, very little current will need to be supplied to the relay, so cost and size should not be a problem.
The current injection into the relay of up to10 amps will be more of a challenge than the voltage input. This current could be controlled by voltage or resistance to ground. One problem with this circuit will be power dissipation. Smaller voltages that the 110VAC offered by the supply will need to be used to solve this. A step down transformer with a ratio of 120:12 and a VA rating of 250 or more will be required. Current could now be controlled by using power rheostats and resistors. The exact configuration of these resistors is important. To simulate a fault, a small current could be injected to the relay and then a larger fault current added to this. Two variable resistances in parallel would work for this. These resistors would need to dissipate up to 100 watts of power.
Here is a preliminary drawing of what the source circuits would be:
Analog voltage and current meters will be used to measure our supplied voltage and injected current.
Besides supplying the relay with voltage and current, the breaker will need to be simulated using relays. These relays must have enough contacts to stop the current being injected into the SEL as well as provide an input to the SEL.
Drawings
Panel Layout
Power Schematic
Control Schematic
Documents
Requirements Capture (10-08-06)
Requirements Capture (REVISED)
Project Progress
Front Panel Decal (18" x 19")
Pictures During Construction
Front Panel COMPLETE (3-15-07)
Project In Action
SEL Event Report - Overcurrent Element
The data to make this chart was stored in the SEL Relay after the event. This can be downloaded from the relay using SEL's AccSELerator software. The vertical line shows when the trip output operated.
