American Innovations MicroMax GPS360, Руководство пользователя

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D
Interrupters User Guide 61
Appendix D: Mercury Relay Advisory
The information in this section is intended to notify American Innovations (AI) customers of the
manufacturer's published limitations on mercury relays.
Customers primarily purchase mercury relays for use with current interrupters. Current interrupters
provide great programming flexibility to enable customers to use a wide variety of interruption
cycles.
AI supplies mercury relays from a variety of respected and reliable vendors including MDI and
American Electronic Components (AEC). These manufacturers publish expected relay lives of 3 to 6
million cycles depending upon the type of relay selected. AEC, the manufacturer of Durakool relays,
indicates that relay life will be significantly shortened at rates exceeding 1,500 cycles per hour. MDI
recommends no more than 900 cycles per hour. Depending upon the interruption cycle chosen by
the customer, it is possible to exceed the manufacturer's recommendation, which would result in a
likely reduction of service life.
As an example, customers who elect to use mercury relays to interrupt at 1 cycle per second will
generate 3600 cycles per hour. Customers should consult the manufacturer's documentation to
select the appropriate relay for the application.
Durakool information can be found on the AEC web page at the following address:
http://www.aecsensors.com/html
In the Durakool documentation, the following two situations are explained that may impact the
current carrying capacity of the relay: 1) cycle rate and 2) voltage values. The sizing tables indicate a
methodology for determining the maximum amperage that can be carried depending upon the
cycle rate. An additional derating table for mercury relays is provided for those instances where
voltage in excess of 48 V DC is being interrupted. When selecting relays, customers should be aware
of both of these derating tables to choose the best relay for the application.
To avoid depolarization of the CP system, the mercury relays we sell that AI sells are of the normally
closed variety. It is possible that a normally closed relay will fail at the end of its life in the open
position due to a malfunction of the spring mechanism which drives the plunger/contacts into a
normally closed position. If this occurs, a depolarization situation would result. AI has the following
two recommendations:
1.
Customers using mercury relays should consider periodic replacement of these relays based
upon engineering estimated life via a preventive maintenance program to reduce the
likelihood of an open circuit failure.