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High voltage vacuum relays. Basic terms and definitions.

Arc – electrical discharge between mating relay contacts when the circuit is interrupted under voltage.

Contact chatter - Intermittent unwanted opening of closed contacts or closing of open contacts.

Gap - opening closed contacts to interrupt the electrical circuit.

Voltage breakdown - an undesirable condition for the occurrence of an arc in the relay due to overvoltage.

cold chain - de-energized electrical circuit.

Dielectric - an insulating medium capable of recovering in the form of electrical energy all or part of the energy necessary to create an electric field (voltage). The electric field strength is accompanied by displacement or charging currents. Vacuum is one of the best dielectrics.

hot chain - the electrical circuit is energized.

closure - Closing open contacts to close the electrical circuit.

Peak test voltage — Peak AC voltage (at 60 Hz) that can be applied between external high voltage terminals or between an open terminal and ground for one minute without any indication of failure. The peak test voltage must not be exceeded even for very short pulses.

Rated operating voltage (peak kV) is a voltage that can be safely applied to the relay for extended periods of time without failure. This nominal voltage decreases with increasing AC frequency. The rated operating voltage approaches the peak test voltage only at lower frequencies.

D.C – Current that flows through closed relay contacts for extended periods of time. This rated current is determined by the temperature rise of the relay sheath. The ceramic relay allows temperature rise up to 100°C. Current performance can be increased by external cooling such as forced air or radiators.

contact capacitance is the capacitance of the relay, measured between (a) open contacts or (b) between a contact and ground. Measured at 1 kHz.

contact resistance is the resistance between closed contacts, measured at 6.0 VDC and 1.0 A rms load.

Response time is the time in milliseconds between the first energization of the relay coil and the final closing of all normally open contacts, including contact rebound.

Release time is the time in milliseconds between de-energizing the relay coil and the final opening of all normally closed contacts, including contact rebound.

Ambient temperature range - the range of ambient temperatures at which the relay installed in the equipment will safely operate. The heat will be generated by the current flowing through the relay, which will raise the temperature above the ambient temperature depending on the set current level.

Pull-in voltage - the minimum coil voltage required to operate the relay so that all normally open contacts close.

Reset voltage - the maximum coil voltage at which the relay is activated and all normally closed contacts are closed.

Coil resistance is the DC coil resistance in ohms, measured at 25°C.

Hit is the amount of g (gravity) that the relay can withstand when tested with a sinusoidal pulse (calibrated shock) for 11 milliseconds without opening closed contacts or closing open contacts.

vibration peak is the maximum harmonic movement at rated force and frequency that the relay can withstand without uncontrolled opening of closed contacts or closing of open contacts.

Expected mechanical life - the number of operations in which the relay can reliably operate. Cold switch applications approach this figure.