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Numerical Single Function Relays : Genesis->
Numerical Volts/Hertz Protection Relay Type : MBT 191


Nominal Voltage and Frequency:

MBT 191 relay can be connected either in phase -phase or phase - neutral PT secondary circuit. Nominal voltage which is settable (50 -150 V) in the relay could be chosen according to the connection. And the nominal frequency is settable either as 50 or 60 HZ.

Two Elements:
MBT 191 relay consists of two elements. Each element can be independently put off or set to a wide range of overfluxing setting (b1 and b2). Both elements are having definite time characteristics and four types of inverse characteristics. Each element is provided with two numbers of ^N/O^ contacts independent to each other.
Both elements can be selected appropriately to give two stages of protection for the equipment. In addition to these two elements, starting function of these elements are indicated by a starter LED and a changeover contact is available for annunciation.

Multiple Characteristics:
Both elements are provided with definite time characteristics (DTL) and four types of inverse characteristics.

Cooling Time Delay:
This relay also has resetting time feature. After trip occurs due to over fluxing, till the resetting time delay (which is settable in the relay) the starter indication will be on and the relay cannot be reset. Only after resetting the relay the breaker has to be closed again. This feature gives enough cooling time, which is necessary to cool the equipment when any over-excitation occurs and before it is restored again into the operation.


  • Power Transformers
  • AC generators
Standard Features
Numerical, true RMS measurementBoth DC & AC auxiliary supply available
Drawout modular case (150X151mm cutout )Compact design
Non-volatile memory for trip indicationSelf-monitoring facility
7 segment LED displayStatus indication LEDs
Sealable front cover to prevent unauthorised access6 output contacts
Volts/Hz (Over-fluxing) (24)2 Stage V/F setting
160 inverse curve characteristics in addition to definite time lagInbuilt adjustable cooling/resetting time delay
1 status input for blocking
MBT 191.pdf

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