NEMA US G 112-2021 电容器组采购规范指南

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US G 112-2021

Capacitor Bank Purchasing Specifications Guidance

Disclaimer

The Standards or guidelines presented in a NEMA standards publication are considered technically

sound at the time they are approved for publication. They are not a substitute for a product seller’s or

user’s own judgment with respect to the particular product referenced in the Standard or guideline, and

NEMA does not undertake to guarantee the performance of any individual manufacturer’s products by

virtue of this Standard or guide. Thus, NEMA expressly disclaims any responsibility for damages arising

from the use, application, or reliance by others on the information contained in these Standards or

guidelines.

NEMA US G 112-2021

Page 2

CONTENTS

Introduction.................................................................................................................................................... 3

Standards ...................................................................................................................................................... 3

Cost Considerations ...................................................................................................................................... 6

Capacitive Mvar Required ............................................................................................................................. 6

Choosing a Voltage Rating for the Capacitor Bank ...................................................................................... 6

Physical Arrangement of Stack Racks .......................................................................................................... 7

Unit Size ........................................................................................................................................................ 7

Rack Configurations ...................................................................................................................................... 7

Electrical Bank Configurations ...................................................................................................................... 7

Considerations in Overvoltage Operation – Switchgear Limitation............................................................... 8

Closing .......................................................................................................................................................... 8

NEMA US G 112-2021

Page 3

Introduction

There are many aspects that must be considered in designing and specifying capacitor banks. The

equipment electrical ratings, physical arrangement, and relay protection scheme are intimately intertwined.

The bank must be designed to accommodate all applicable devices such as instrument transformers,

capacitor switches, protective relays, fuses, and bus-work, along with other devices specific to the

application. Capacitor bank protective schemes must be designed and applied to provide the signals

required for protective relaying to perform as expected.

This document provides guidance to help engineers draft comprehensive and clear purchasing

specifications for capacitor banks. After providing an overview of the relevant Standards, and sections

within those Standards, we provide helpful information to assist with cost-impact analysis and

considerations for product ratings, rack designs, and bank configurations.

Standards

When drafting purchasing specifications, users should reference several relevant Standards:

IEEE 1036 Application Guide for Shunt Capacitors

Section 5.2.3.1 covers overvoltage-specific capabilities. This is important to protect capacitors from

overvoltages beyond their capability. Each overvoltage has an expected number of occurrences per year.

Relay protection can be relied on for the longer duration overvoltages, but the short-time occurrences

may require surge arrester protection.

Section 5.2.3.2 on overcurrent capability serves as a guide if some type of limitation is needed to prevent

excessive discharge currents during switching or closing faults. In addition, it provides suggestions for

grounding methods to direct high current transients out of the ground grid. The section also gives some

details on switchgear that can be used for capacitor bank switching.

Capacitor Standard IEEE 18 lists capacitor unit capability of operation of 110 % continuous overvoltage.

That capability is for contingencies such as temporary overvoltage from fuse operation or element failure,

with the expectation that the user will soon correct the overvoltages.

IEEE 18 Capacitor Standard

One key section is section 7.1 Design Tests which determines the unit’s overvoltage and overcurrent

capabilities. This section also specifies the major case insulation performance capability. The production

tests of Section 7.2 are essentially quality control to ensure that defective units do not get shipped to the

customer.

Another key section is 6.9, which provides physical dimensions for substation equipment.

IEEE 18 specifies certain physical dimensions for capacitor units, such as spacing between bushings and

the mounting hole spacing. The spacing between bushings determines the maximum unit voltage rating,

which is typically 20kV for two bushing units and 25kV for single bushing units. The design maximum

altitude is 1800m for normal service conditions. IEEE 18 also specifies that capacitor racks utilize 8” unit-

to-unit spacing up to 8kV unit voltage; 9” unit spacing up to15 kV unit voltage; and 11” unit spacing above

15kV. The mounting channel dimensions are also specified.

IEEE C37 Series

IEEE C37.012 is an application guide for Circuit Breakers switching capacitive loads.

IEEE C37.100.2 contains the common requirements for testing capacitive current switching devices.

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摘要：

NEMA US G 112-2021《电容器组采购规范指南》围绕电容器组的采购要求、技术参数、试验验收与合规要点提供标准化参考，适用于电力工程、无功补偿及工业配电项目的规格书编制、供应商比选和质量控制，帮助用户快速理解该标准并提升采购效率与合规性。

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