Capacitor Bank Protection

Do your capacitor banks suffer from one of these issues?

  • Frequent protection element misoperation causing downtime
  • Time-consuming investigations to determine whether or not a problem is present in the bank
  • High maintenance costs to discover and replace faulted elements

These problems are often related to the limits of the voltage differential element (87V), more commonly known as unbalance protection. Such nuisance tripping is followed by an arduous maintenance process, one where the entirety of the bank is searched for faulted capacitor units.

Let the ALP protection relay enhance the coverage of your protection scheme: complement your voltage differential element with an impedance-based protection element (21C). This strategy will help you reduce nuisance tripping, improve bank health monitoring and reduce maintenance costs. This element has a better sensivity to detect faults and provides valuable information to better target the maintenance of capacitor banks.

US Patent No. 11,525,850

  • Applicable to fuseless, fused, grounded and ungrounded systems
  • Better localization of the shorted section, reducing maintenance time
  • Better availability of the bank because the protection discriminates between capacitor failures in one string versus capacitor failures spread through the bank
  • Protection not affected by bus voltage variations
  • Immune to temperature variations and to temperature gradients in the bank due to an advanced temperature compensation algorithm (patent-pending)

Hardware configurations

  • ALP-2000: Combination of twelve (12) current and voltage inputs, six (6) digital inputs, four (4) relay outputs, two (2) high-speed power outputs, up to four (4) fiber Ethernet ports


  • ALP-4000: Combination of twenty-four (24) current and voltage inputs in a single device, sixteen (16) digital inputs, sixteen (16) relay outputs, eight (8) high-speed power outputs, up to four (4) fiber Ethernet ports

Main characteristics and advantages:

  • Includes ANSI functions 21C, 24, 27, 50, 50N, 51, 51N, 59, 67, 81, 81R, 87T and LOV
  • Allows protection of up to 18 capacitor bank strings
  • Platform built with the most cutting-edge technologies, resulting in very high processing and storage capacities
  • Better precision of analog readings
  • One of the highest sampling rate in the industry, enabling precise recording and analysis of faults
  • Secure, rugged and reliable protection relay, in compliance with the latest utility standards
  • Protection, automation, metering and monitoring functions built into a single product
  • User-friendly interfaces and software for easy engineering, configuration, commissioning and operation
  • Flexible solution for the detection and processing of non-conventional electrical phenomena
  • Secured WEB server for easy and safe access to the relay settings, real-time measurements and oscillography recordings
  • DNP3 Communications over Fiber Ethernet
  • Optional support for IEC 61850 (MMS and GOOSE)
  • Optional support for an IEC 61131-3 programmable logic controller (PLC)