Transferring Inductive Type Loads

John J. StarkMarketing Services Coordinator, Russelectric Inc.

(Refer to Russelectric Technical Brief: “Eliminating Power Transients When Switching Large Inductive Loads”)

In Phase MonitorVS

Dual Operator

For Switching Inductive Loads

• Russelectric Recommends Dual Operator

But, lets discuss both…

In-Phase Monitor for Switching Inductive Loads

or for Proper Closed Transition Switching(between two available sources)

In-Phase Monitor, Principal of Operation

A feature within the controller (or a synchro-check relay in old designs) where voltage values from source one and Source two are monitored through input signals to the controller. The controller compares the two voltage levels and phase relationship between the frequencies of both sources and will allow a transfer only when the voltage and frequency (of both sources) are within acceptable limits.

Typical set points:5% - 20% nominal voltsPhase angle adjustment: 6 – 20 Electrical degrees

Source 1 Source 2

ATSATS

In-Phase Monitor for Switching Inductive Loads (between two available sources)

Pros:• With some manufacturers this feature can be a significant cost savings over dual operator.

Cons:• Introduces more sensitive and adjustable electronics and circuitry into the system.

ATS

• If an acceptable window of voltage and frequency is not achieved, desired transfer will not happen. Example: ATS needs to return to utility after being in the engine generator (emergency) position… engine speed running erratically, no window achieved… switch in remote location… ATS remains on generator until it runs out of fuel.

N

E

LL

N

E

The load source is disconnected for an adjustable period to allow regenerative power to decay

Operator #1drives thenormal source contactsopen

1

Operator #2then drives the emergencysource contactsclosed

2

N

E

L

Dual Operator Switching for Inductive Loads (open transition, between two available sources)

Dual Operator for Switching Inductive Loads

(open transition, between two available sources)

Pros:• Very reliable. Positive transfer without reliance on sensitive monitors. The switch will always transfer without the load experiencing a “bump”.

• With an inherent dual operator design, ATS has an ancillary benefit in that it can also be used as a dynamic load shed device, completely controllable, either automatically, manually or in a control scheme.

L

N

E

ATS-1

Life Safety &SupportBranches

ATS-2

CriticalBranches

ATS-3

EquipmentBranches

G

E

G

E

G

E

EmergencyDistributionSwitchgear

GeneratorControl &SynchronizingSwitchgear

UtilityDistributionSwitchgear

LoadControl

Circuitry

UtilitySource

G

E

Loss ofEngine #1

ATS - 3 ShedsNon-Critical Loads

Dual Operator for Switching Inductive Loads

(open transition, between two available sources)

Cons:• Depending on the

manufacturer this can be an expensive solution.

L

N

E

• Slight delay on transfers

Power Control People

You Can Rely On!