Paralleling Generator Set Systems and Design

Overview

For each strategy the paper sets out functions, typical applications, advantages and drawbacks across cost, flexibility, redundancy, factory testing and site-integration burden. On-set controls are positioned as low-cost for simple LV island systems, controls-only for MV/HV and retrofits, and integrated switchgear as the most flexible and redundant choice for complex or utility-paralleled systems.

On-generator controls provide dead-bus arbitration, auto and manual synchronising, kW and kVAR sharing, load shed and add, and optional load-demand set cycling. They are typically limited to low voltage (under 600 V); MV uses remote controls-only arrangements. The connecting switching device needs about a 5-cycle close and open time to avoid out-of-phase paralleling, and without master controls these systems are mostly limited to an isolated common bus or a single generator to utility.

Controls-only solutions typically lack utility-grade protective relays and must be wired to the distribution switchgear on site. Integrated paralleling switchgear allows redundant PLCs, networks and relays, factory integration testing and metal-clad, arc-resistant construction, at higher cost.

Key points

1. Three strategies: on-set controls, controls-only panels or PLCs, integrated paralleling switchgear.
2. On-set paralleling is typically limited to under 600 V; MV needs remote controls-only arrangements.
3. The connecting device needs about 5-cycle close/open speed to avoid out-of-phase paralleling.
4. Without master controls, on-set systems are mostly limited to an isolated common bus or one generator to utility.
5. Controls-only solutions lack utility-grade protective relays and need site interconnection to distribution switchgear.
6. Integrated switchgear offers redundant PLCs, networks and relays, factory integration testing and arc-resistant construction.

Using it in design

• Build an architecture selector with the three options and show consequences: LV-only limit for on-set, required breaker closing speed, and master-controller need for complex sequences.
• For MV generator plants or utility-paralleled designs, default to controls-only or integrated switchgear.
• For Tier IV or other high-redundancy designs, prompt for redundant PLCs and protective relaying.

Who should read it

Electrical designers choosing a paralleling architecture and specifiers of paralleling switchgear.

Related standards

• NFPA 110
• UL 1558
• IEEE C37.20.2

Publication details

Authors

Don Dentino

Publisher

Caterpillar

Year

2018

Document number

LEXE1365-01

Document language

English

Source type

Manufacturer

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation