Diesel Generators in the Data Center - When is the Bigger the Better?

Overview

The paper makes two linked claims. Larger sets cut footprint, installation and maintenance cost, and paralleling reduces stranded capacity and makes N+1 or N+2 redundancy easy. For a 10 MW outdoor plant, 3.5 MW sets need two fewer generators and about 1,500 ft2 (140 m2) less land than 2.0 MW sets.

Annual maintenance for 10 MW in Table 1 is $47,614 for 7 x 1500 kW, $43,940 for 5 x 2000 kW and $31,854 for 3 x 3500 kW. The author also cites an independent risk study of a 12 MW N+1 plant in which fewer, larger sets show a lower system failure probability, because the most probable failures involve auxiliary equipment rather than engines or alternators.

Three concurrently maintainable paralleling topologies are described. A segmented bus with tie breakers can isolate one gear section in an N+2 plant while keeping N, and bus-differential relaying removes the bus as a single point of failure. A dual bus gives each generator its own transfer arrangement. The 'three to make two' scheme parallels load buses A and B so any one generator or switchgear item can be maintained with N still available.

Key points

1. At 10 MW outdoor, 3.5 MW sets save two generators and about 140 m2 versus 2.0 MW sets.
2. Annual maintenance at 10 MW: $47,614 (7 x 1500 kW), $43,940 (5 x 2000 kW), $31,854 (3 x 3500 kW).
3. An independent 12 MW N+1 risk study shows lower failure probability with fewer, larger sets.
4. Most probable failures are in auxiliaries, not engines or alternators.
5. Listed paralleling benefits: efficiency, reliability, redundancy, transient performance, scalability, serviceability.
6. Segmented bus with tie breakers isolates a gear section in N+2 while keeping N.
7. 'Three to make two' (N+1) parallels load buses A/B so any single generator or gear item can be serviced with N available.

Using it in design

• Compare candidate set sizes on count, footprint, install and maintenance cost for the target N+x, preferring fewer larger sets where the site allows.
• For segmented bus, dual bus and three-to-make-two templates, verify that removing any one generator or gear section leaves at least N.
• Direct reliability effort at auxiliaries such as fuel, cooling and controls, since those dominate the failure modes cited.

Who should read it

Electrical designers and decision makers sizing and choosing the topology of a data-centre standby generator plant.

Related standards

• Uptime Institute Tier Standard: Topology

Publication details

Authors

David Matuseski

Publisher

Cummins

Year

2015

Document number

Power Topic #6064

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