Functionality - ABB 615 series Technical Manual

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1MAC059074-MB A

615 series ANSI

Technical Manual

Functionality

The voltage vector shift protection function 78V, also known as vector surge or delta phi

function, measures continuously the duration of a voltage cycle. At the instance of

islanding, the duration of measured voltage cycle becomes shorter or longer than the

previous one, that is, the measured voltage cycle shifts with time. This shifting of voltage

is measured in terms of phase angle. 78V issues an instantaneous trip when the shift in

voltage vector exceeds the set value.

The function can be blocked with BLOCK input. Blocking resets timers and outputs.

Operation principle

The function can be enabled and disabled with the Operation setting. The corresponding

parameter values are "Enable" and "Disable".

The operation of 78V can be described by using a module diagram. All the modules in the

diagram are explained in the next sections.

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Functional module diagram

Vector shift detector

This module measures the duration of each cycle of the voltage signal phase. The duration

of the present cycle is compared to the previous cycle, considered as reference. When the

mains is lost, a sudden change is seen in the cycle length, if loading of the generator

changes suddenly and power mismatch or unbalance (generation vs. load) in the islanded

part of the network is large enough. The cycle shifts with time, that is, the frequency may

not change but a vector shift is seen in phase as shown in

This step is measured in degrees for each voltage signal defined by the Phase supervision

setting. The Phase supervision setting determines which voltage is used for detecting

vector shift. The available Phase supervision options are "All" and "Pos sequence". If the

calculated value of Δδ exceeds the set Pickup value setting for all the defined phases, the

module sends an enabling signal to start the Pulse timer.

The Voltage selection setting is used to select whether the available voltage signal is

phase-to-ground or phase-to-phase voltage.

Protection functions

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