e-VT Guard
The e-VT Guard is an active damping device for MV inductive voltage transformers (VTs) that manages instances of ferroresonant over voltage.
The device applies an immediate and effective resistive damping when a ferroresonce event occurs without creating excessive consumption (as is the case when permanent damping resistors are used).
The e-VT Guard connects directly to the secondary terminals of a VT and can be installed on any VT*.
Features
- Damping resistors are applied to the VT secondary for a short period of time (100 ms). Afterward, they are gradually disconnected over a period of 100 ms to reduce the chance of ferroresonance reignition.
- LED indicator that blinks every 5 seconds to signal operational device status. The blinking pattern changes every time the e-VT Guard successfully dampens a ferroresonance event. The change in pattern allows a visual indication of the number of times the e-VT Guard has detected and successfully dampened a ferroresonance event in the last 48 hours.
- Optional 5 second delay for applications with relay protection devices.
- Digital relay output that can be connected to a controller, meter, or other device capable of receiving the signal. This signal will pulse each time a ferroresonance event is detected and successfully dampened.
- Single phase connection.
- If the e-VT Guard is unsuccessful in damping a ferroresonance event after three attempts, the LED blinking scheme will change to an alternating red/green pattern to reflect this condition. The modified blinking scheme will remain in place for 48 hours of continuous power; after which it will reset back to normal. However, should the device lose power during this window of time, the modified blinking pattern will resume after the unit restarts and the 48-hour time period resets. In addition to the visual indication change, three consecutive pulses will be generated across the relay contacts.
- When only a single relay input is available, the relay contacts of three e-VT Guard units can be connected in parallel and wired to the relay, controller, meter or other device.
- Indoor and outdoor rated (with the inclusion of the extended junction box cover).
Technical specifications
| Rated operation voltage | Vr | 100-130 V |
| Max operation current | Imax | 24 A/0.2s |
| Relay contact voltage | Vc | 125 V AC (Max. 100 mA) 30 V DC (max. 100 mA) |
| Nominal frequency | fn | 50/60 Hz |
| Optional damping delay | td | 0s/5s |
Operating ambient temperature: -40°C to +75°C
Storage and transportation temperature: -50°C to +85°C
Humidity: up to 90%
Max altitude: 2000 m
Pollution Degree: 1
Certifications and standards
The e-VT Guard has an IP20 protection class, IP54 with extended junction box cover.
The e-VT Guard is UL 61010-1 certified.
* The e-VT Guard requires connection to an individual transformer with secondary voltage taps configured for 115V-120V, one e-VT Guard unit per voltage phase. This device is not designed be connected phase to phase across two transformers.