Blown fuse detection on ungrounded-split-wye connected capacitor bank is accomplished with an over-current relay and current transformer as shown above. This protection system is not susceptible to system unbalances, but leads to complexity in bank design. This system is recommended for larger single stage metal-enclosed capacitor banks and harmonic filter banks.

Blown fuse detection of ungrounded banks is accomplished with an over-voltage relay and a neutral voltage sensor or potential transformer. This detection method is simple and economical, but is susceptible to system unbalances.


Blown Fuse Protection
System

NEPSI's Metal-Enclosed Capacitor Banks and Harmonic Filter Banks come equipped with a blown fuse protection system. This system is developed based on IEEE Std. C37.99-2000, IEEE Guide for the Protection of Shunt Capacitor Banks (Revision of IEEE Std. C37.99-1990). A blown fuse protection system provides the following key functions:

  • Provides indication to maintenance personnel that a fuse(s) has blown. If requested, a strobe light or dry-contact is provided for remote indication.
  • Protects the remaining capacitors (capacitors without blown fuses) from overvoltages due to neutral voltage shift. This is important in all ungrounded-wye connected capacitor banks.

As standard in multi-stage capacitor banks, NEPSI provides one protection system for the entire bank. For large banks and for improved reliability, NEPSI recommends each stage of multistage banks be equipped with a blown fuse protection system. By equipping each stage with a blown fuse protection system, the following benefits are obtained.

  • The overall bank has a higher reliability as only a part of it is tripped off-line for a blown fuse.
  • Voltage disturbances are less during tripping operations as a smaller portion of the bank is tripped for a blown fuse condition.

If not specified in the RFQ or purchase order, NEPSI will typically provide a protection system and bank configuration that is most economical.

Northeast Power Systems, Inc.
66 Carey Road
Queensbury, New York 12804
Phone: 518-792-4776
Fax: 518-792-5767

E-mail: sales@nepsi.com
Website: www.nepsi.com


NEPSI's capacitor banks and harmonic filter banks are typically connected in an ungrounded-wye connection with voltage sensing as shown above. A blown capacitor fuse will result in a neutral-to-grounded voltage. Other connections and protection methods are available upon request.

Blown fuses detection on grounded-wye connected capacitor banks is accomplished with a neutral CT and over-current relay as shown above. The bank does not need to be tripped off as in ungrounded banks as capacitor voltage does not rise as fuse operate.

 

Goto to the following NEPSI Tech-note for more information on unbalance protection of ungrounded-wye connected capacitor banks.

www.nepsi.com/neutvlt.htm