KPF221 Frequency Protection for Single or Three Phase Systems

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Frequency Protection for Single or Three Phase Systems
KPF221x Brochure



Frequency Guard for Single or Three Phase Systems


  • Precision High / Low Frequency Protection
  • Ranges 45-55, 55-65 and 45-65Hz
  • Quartz Controlled Frequency Protection and Meter
  • Definite time trip delays
  • Complies with G59 requirements
  • Optional very fast analogue output (<50mS), (F-versions)
The digitally controlled KPF221x provide precision (0.2%) high/low frequency protection.
A digital, crystal controlled frequency window discriminator controls operation and delay of the frequency low/high alarm relays. The unit measures the zero point crossing of the voltage true r.m.s. value, and accuracy is independent of any wave form distortion.
The auxiliary voltage is supplied from the unit voltage input. A DC auxiliary voltage input is optionally available. A green LED indicates POWER on. Start of monitoring function is delayed when power is switched on (default 2 secs delay). In this way false tripping during power up is avoided. The precision DIN96 meter reads the frequency directly in Hz, and has low-reflection glass to ease reading at a distance.
The frequency meter and the triple-zone status LEDs at a glance gives the clear safety message:
The unit has C/O relay outputs for Frequency High Trip (R1) and Frequency Low Trip (R2). A trip LED flashes when the trip level is passed, the relay trips after elapsed delay. The frequency differential set points can be user-adjusted to suit most applications. Trip levels and delays are settable on unit rear.
Red alarm lamps FREQUENCY LOW or FREQUENCY HIGH flash instantly (approx. 1 flash per second) on passing the frequency differential set points. The lamp changes state and the alarm relay operates after the pre-set delay. If a fault condition ends during the delay interval, the timer will automatically reset.
The F-versions have an fast response milliamp output signal proportional to the Hz range.

Additional information

Weight 2 lbs
Dimensions 9 × 9 × 9 in

KPF221E Frequency Protection, Non-Latching Output, without Analog Output, KPF221G Frequency Protection, Latching Output, without Analog Output, KPF221F Frequency Protection, Non-Latching Output, with Analog Output, KPF221GF Frequency Protection, Latching Output, with Analog Output


45-55Hz, 55-65Hz, 45-65Hz

Monitored Voltage

100-120VAC, 200-240VAC, 380-415VAC, 440-480VAC

Aux Supply

No Aux Supply, 12-24VDC Aux Supply, 48VDC Aux Supply, 110VDC Aux Supply

Analog Output

No Analog Output, 0-10mA, 0-20mA, 4-20mA, 0-10VDC