ABB Dynamic inrush restraint for applications with downstream transformers

Dynamic inrush restraint for applications with downstream transformers

Inrush currents degrade power quality Static Transfer Switches (STSs) are essential

components in data center power system configurations. Mainly relying on transformers

primary side switching, these devices are the bridge between the power sources and the power

distribution units. This architecture offers many advantages to the customer in terms of smaller

footprint and lower costs; however, if not properly switched, high transient inrush in downstream

transformers will occur.

The inrush currents produced degrade the power quality of the preferred source, overload upstream

UPSs and trip protective circuit breakers. The inrush currents can also create intolerable forces in

the windings, which in turn reduce the lifecycle of power transformers as these currents can reach

the short circuit rated value and can last many cycles before they dissipate.

Real Time Flux Control™ for DIR With state of the art digital signal processors and a

newly developed algorithm, an innovative approach was created called Real Time Flux Control™ for

dynamic inrush restraint (DIR.) Using advanced Real Time Flux Control, SuperSwitch®4 can

dynamically monitor and adapt its transfer switching to account for any variation or condition

that may occur during an upstream outage. Real Time Flux Control enables out of phase transfer

times that are 25% faster and inrush currents that are 40% lower than previous generation systems.

By controlling inrush currents, the SuperSwitch®4 protects upstream and downstream infrastructure

from the harmful effects of excessive currents.

This technology is an intelligent proprietary method that makes no compromise to the voltage

output for mission critical applications by providing a performance that exceeds the CBEMA

and ITIC standards, regardless of phase drift between sources.

How does it work?

The STS constantly monitors the power quality of both sources taking into account the customer

specified thresholds. In addition, three transfer modes are available to customers to choose from:

A9. DIR always and DIR limited.

A9: this mode is a proprietary method that is to be used only when the phase difference between the

sources is less than a user defined phase angle.

The range of this setting is adjustable up to +/– 30 degrees, and is not recommended for larger phase

differences.

DIR always: this mode allows the SuperSwitch®4 to permanently transfer using the Real Time Flux

Control approach and should result in low inrush regardless of how far the two sources are out of

phase.

DIR limited: this mode is the recommended setting for the SuperSwitch®4. In this mode, a hybrid

approach of A9 and DIR is performed depending on the phase difference between the sources.

Most customers use the recommended setting of DIR limited because the STS will auto select when,

and if, the DIR function is needed depending on the phase difference as illustrated by Figure 1 below.