Electrical machines & devices are made to work on optimum efficiency at particular voltage range. Below the permissible voltage range machines do not work precisely & Their overall efficiency decreases. In worst cases, machine get damaged.
That’s why voltage stability is important. Voltage stability not only provides the optimum output, It also increases the useful life of the machine.
To prevent the voltage fluctuation, Voltage stabilizers are there. But chances of Voltage fluctuation is always there That’s why there should be some sort of provision that; an indication should be there or a tripping should be there whenever voltage dips below the permissible voltage range.
There are multiple voltage monitoring devices with extra features. But one function of all these voltage monitoring devices remains the same. That is; These devices continuously monitors the voltage. Whenever voltage goes beyond the range, An alarm is get triggered through an electromechanical relay.
To understand better these under voltage relay, Further next, Under voltage relay made by TEKNIKA is been discussed.
UNDER VOLTAGE RELAY
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This under voltage relay continuously monitors the voltage present on the line. This relay also contains the selectable timer. When monitored voltage get lie under the preset voltage value than timer starts counting, After complete timing changeover relay get operated.
When monitored voltage dips below the selected value or power goes off, changeover relay get deenergized which further produces a command to the signal circuit or trip circuit.
This relay can also be used to add another energy source in the circuit when one of the energy source breaks off. Like energizing the Electrical generators when power from local utility get cut out.
FEATURES
- For voltage setting, easy variable knob is been provided ranges from 300 TO 400Volts.
- Timer for tripping delay ranges from 0 to 10Sec.
- Total three indicators- Supply, Fault & Healthy indication.
- 2 changeover relay each having a capacity 6Amps,230VAC.
- No Auxiliary supply required.
- No Neutral required, Only 3 phase supply required for device working & monitoring.
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CONNECTIONS IN DIFFERENT APPLICATIONS
In this relay, there are two things:
- Only measurable 3 phase supply; No Auxiliary supply; is required in this device. (Described in an image below)
- 2 Changeover relays have been provided for control circuit. (Described in an image below)
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1. Connections for AMF panel
” Automatic mains failure(AMF) panel as name suggest specially designed for power failure conditions so that when power goes off; Alternate energy source like diesel generator get connected with the circuit. “
Undervoltage relay plays an important role in AMF panel. 3 phase power from power generating utility is connected on under voltage relay.
In normal condition, When Voltage is higher than the preset value; relay of UVR operates. At such condition, Common contact get connected to NO contact.
In abnormal condition, Such as one phase missing or voltage below the required level or no voltage; UVR produces a fault indicator in along with changeover relay get deenergized. In such condition, common contact get connected to NC contact.
Connection diagram for AMF panel been explained below:
Here in this circuit, There are two modes Auto mode & Manual Mode. In Auto mode, DG get started automatically when power from power utility goes off. While in Manual mode, ON & OFF push buttons are utilized for DG start & DG stop.
Three phase power from power utility is directly connected to the UVR. DG relay which is having a coil voltage of 230VAC. Neutral is directly connected to the DG relay & only a red control phase is working.
Red phase first passes through the selector switch which is basically a 3 way selector switch. When switch is in auto position, phase passes through the NC contact of the UVR than it directly connected to DG starting relay. Which means in Auto mode, In abnormal voltage conditions through NC of changeover relay, DG get started automatically.
When switch is in manual position, Control phase passes through the NC (stop) contact & than NO(start) contact. For relay holding, relay’s NO contact is connected parallel to the NO(start) push button. At last, phase is connected to the DG relay.
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2. Connections for the safety of Induction motor running with DOL Starter
In Direct online starter(DOL), Motor directly connects to power supply without any change in voltage, Frequency & terminal connections that’s why known as Direct online starter. In this motor terminals & Power supply are connected across the contactor. When contactor get energized, motor get energized.
This under voltage relay is used as protection, Protection from under voltage. As we had discussed, changeover relay only operates in healthy conditions That’s why NO contact of the UVR is utilized in this circuit.
The circuit diagram explained below:
Having a contactor’s coil voltage is 230VAC. Neutral is directly connected to the contactor & a single red phase work as a control voltage.
According to the circuit diagram, Control phase (RED) passes through the NO contact of the changeover relay than it passes through the NC contacts of overload relay & NC (stop) push button. Than It passes through the NO(start) push button. For contactor holding, NO contact of contactor is connected parallel across the NO(start) push button. At last, control phase is connected to the contactor.
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SUMMARY
- Under voltage relay is a safety device. Which continuously monitors voltage Whenever voltage get below the set level, It produces the alarm or trip signal.
- Under voltage relay is needed for two reasons, 1st reason- To get an alarm or tripping when voltage dip below the set range. 2nd reason- To connect another power source when one of the power source get breaks off.
- For alarm or tripping signal, A relay is provided with under voltage relay.
Hope, You like the post if you have any doubt, Suggestion or query please do comments!