Introduction to Medium Voltage Metal Enclosed Capacitor and Filter Banks
Mar 11,2020

Product Description

ZDDQ Medium Voltage Metal Enclosed Capacitor and Harmonic Filter Banks are designed for industrial, commercial, and utility power systems requiring medium voltage automatic power factor correction. Standard designs are available for placement in outdoor or indoor substations (an enclosure integrity option can be added to allow for placement in publicly accessible areas) for power factor correction, loss reduction, and voltage support. The banks come fully assembled and ready for interconnection.

ZDDQ’s standard banks can be modified in most circumstances to meet your specific requirements. Contact ZDDQ( to discuss your requirements and obtain a price quote.

ZDDQ can provide Power System Studies, Engineering Studies, System Design and Start-up/ Commissioning services.

Product Scope

•Voltages from 3kV through 35 kV

•Reactive power ratings to 35,000 kVar in a single enclosure

•Short circuit ratings to 61 kA

•Up to 12 Capacitor Steps in a single bank

•Banks come fully assembled, tested and ready for interconnection

•Integral air-disconnect/ground switch or roll-out circuit breaker

•Integral protection and control system

•Compliant with ANSI, IEEE, IEC, CSA, NEC and NESC codes and standards

Standard Features


Free standing, compartmentalized, all welded, galvanneal steel construction with 3 point pad-lockable latching handles and stainless steel hinges. The enclosure is painted with a corrosion resistant ANSI gray-61 epoxy paint.


Low loss, double bushing capacitors can meet or exceed IEC 871, IEEE 18 and CSA standards. Capacitors are connected ungrounded-wye as standard. Grounded banks are provided on request or for reasons of application. Internal discharge resistors reduce the residual voltage to less than 50 volts within 5 minutes of de-energization. The dielectric fluid is environmentally friendly, biodegradable, non PCB, with low toxicity. Internally fused capacitors are available upon request.

Transient Inrush Reactors

ZDDQ’s Reactors are provided on each stage to limit the frequency and magnitude of inrush currents from back-to-back capacitor bank switching.

Load Interrupter Air Disconnect Switch

Switch is located in a separate compartment that allows the main fuses and other components located within the capacitor compartment to be maintained without having to disconnect power to the bus feeding the bank.

Key Interlock System

Key Interlock system dictates a safe sequence of operation and entry into the capacitor bank.

Ground Switch

An interlocked ground switch is provided to ground the load-side terminals of the incoming air-disconnect switch and/or capacitors for safety during maintenance.

Main Incoming Fuses or Circuit Breaker

Main incoming fuses provide main bus protection and backup protection for capacitors.

Lightning Arresters

Bank is protected from lightning and switching transients with heavy duty distribution class lightning arresters.

Vacuum Switches

Each stage is controlled by long life low maintenance vacuum switches or vacuum contactors (for voltage less than 6.6kV). For switching at 25kV and higher, SF6 switches with or without pre-insertion resistors can be provided.

Individual Capacitor Fusing

To improve bank reliability and protect against case-rupture, each capacitor is individually fused with current limiting fuses.

Potential Transformer

A control power transformer is provided for protection, control and operation of the bank.

Ground and Phase Bus

A 1/4” X 2” Tin plated ground bus is provided through the width of the enclosure to assist in grounding during maintenance. All phase bus is also Tin plated and rated at a minimum of 135% of the bank nominal current rating.

Automatic power factor Controller

Capacitor stages are automatically controlled by one of a variety of controllers that can switch stages on an off based upon current, var load, power factor, temperature, time-of-day, metering pulses, or voltage. Power Factor Control is standard.

Typical Three Line Diagram

Line Diagram of Medium Voltage Metal Enclosed Capacitor and Filter Banks

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