Power Transmission and Distribution

Controlled Switching of High-Voltage Circuit-Breakers

PSD02

Controlled switching

Increased system reliability as a result of reduced voltage uctuations and lower harmonic stress.

Longer service life of equipment by reducing switching over-voltages and inrush currents.

Possible substitution of costly, complex mechanical auxiliary equipment, such as closing resistors.

The intensity of the transients during switching operations depends on the phase position at the point of switching. A circuit-breaker without this unit operates all three phases at approximately the same instant. Due to the arbitrary switching instant and the shifts of the three phases with respect to each other, random phase positions tend to occur. The transients vary accordingly, in the individual phases. Generally, however, unfavorable switching conditions normally occur in at least one phase.

Controlled switching allows for a individual optimum switching instant to be set for each pole. The transients are thereby reduced to a minimum. For circuit-breakers with three independent drives, each pole receives an individual switching command from the control unit.

Controlled switching Less wear and tear on the equipment

Non-controlled closing of a capacitor bank at a voltage peak can result in high inrush currents and over-voltages, which greatly exceed the nominal system values. Consequently, the capacitors are heavily loaded both mechanically and dielectrically which can lead to premature ageing. Resulting destruction may occur in the capacitors. Closing the contact at the optimal point in time, reduces the load on the capacitor bank and improves the quality of the voltage of the network.

When switching capacitive and inductive loads, switching transients occur, resulting in electrodynamic and dielectric stresses on system. These stresses can be minimized by the introduction of controlled switching, which can be provided by the PSD02 control unit from Siemens. This unit offers the following advantages:

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Switching a capacitive load

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Reactors and transformers

Non-controlled energizing of a reactor or a transformer close to the voltage zero crossing, may result in a very high direct current component. The induction generated saturates the iron core and induces an inrush current which results in a high load on the transformer or reactor. Controlled switching at the voltage crest will also prevent switching transients from occurring, thus protecting the equipment. Non-controlled de-energizing of inductive loads such as shunt reactors or transformers means that the circuit-breaker can interrupt smaller currents before the natural zero crossing. This process is known as current chopping

and leads to steeply rising over-voltage. A re-ignition across the open breaker contacts may result, if the isolating distance at this instant is not sufcient to withstand the dielectric load. Over-vol-tages are inevitable. Controlled switching also offers a remedy in this case. Optimization of the open-close operational instant prevents re-ignitions and the over-voltages are minimized. In the cases described thus far, non-controlled making or breaking can lead to increased stress on the equipment. Closing resistors and reactors that were previously used to reduce these stresses may no longer be required. Controlled switching offers an economi-cal alternative.

Front view of PSD device

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Switching a transformer

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The functions and features of the PSD02 control unit

The PSD02 control unit optimizes the phase relative to the cur-rent or voltage of the switching operation of the circuit-breaker by evaluating these gures. Controlled switching takes the current opening and closing times of the circuit-breaker into account. Commands from the protection system are passed directly onto the circuit-breaker. Closing occurs at an optimal phase position relative to the voltage. The phase position is se-lected based on the actual switching duty so that transients can be avoided. When opening small inductive currents, the voltage cycle of the contact separation is such that the contact clearance during interruption is sufcient to prevent re-ignition.

Integration into the substation

The PSD02 control unit is integrated into the substation con-trol system so that the switching commands for operation can be processed. Opening commands that are generated by the protection system in case of short circuit are passed directly onto the circuit-breaker. In such cases the control of the switching instant does not occur.

The functions and features of the PSD02 control unit

The PSD02 control unit offers a wide-range of functionalities. It can select and set the opening and closing instant for each switching pole individually. The PSD02 control unit is suitable for all Siemens high-voltage circuit-breakers, including previ-ously installed circuit-breakers with minimum alteration of the opening and closing time and retain a sufciently steep pre-arc-ing characteristic curve. Two separately congured parameter settings in the control unit make it possible to control a circuit-breaker by carrying out two different switching tasks. A mode input automatically selects between the two tasks during opera-tion. To compensate for possible deviations in the opening and closing times of a circuit-breaker, the PSD02 control unit offers two functions to perform making and breaking at the optimal instant for each pole:

The PSD02 also compensates on the dependence of the operat-ing times on the ambient temperature and the control voltage. In the case of hydraulically driven breakers, the drive energy (hydraulic pressure) is also compensated. Different compensa-tion characteristics are selectable. The PSD02 has a wide range of monitoring and evaluation functions to track the success of the controlled switching operations and its internal functions.

Functions

The following data can be acquired from the unit:

The last four switching operations.

All input and output signals.

Voltage and current time curves.

Process curves of the switching commands (e.g. inputs from the control room and outputs from the circuit-breaker) includ-ing reference contact signals.

Oscillograms are stored in a buffer memory and available even after supply interruptions.

Easy graphical evaluations of all the recorded signals of the switching with the help of windows compatible software.

Individual detection of the positions of the circuit-breaker pole with a monitoring function by means of 4 auxiliary switch inputs.

Data-acquisition of the most important data from approxi-mately 400 events and switching operations by means of the history function. In history, the data is acquired cyclically and is event-controlled and stored in a nonvolatile memory.

An option is available for inputting individual parameter set points for frequency, voltages and temperatures. Alarm signals can then be generated when a set point is exceeded, or not reached.

Output of error messages (alarms), e.g. if a switching opera-tion is not successfully performed, or if no zero crossing of the reference voltage has been detected, including an input signal that has not been received.

Monitoring of sensors, hardware, and the voltage supplies.

Experience

Many years of experience in the use and development of control units have gone into the development of the PSD02. This control unit has been subjected to comprehensive electrical, mechanical, and climatic tests. The EMC test in accordance with IEC 61000 and IEC 60255 and the test for low noise emission in accordance with EN 55011 have been passed successfully. Climatic and mechanical tests in accordance with IEC 60068 and IEC 60255 demonstrate unlimited functionality even under disruptive environmental inuences.

Back view with straight through current transformers

Main features at a glance

One device for all switching

Unrestricted parameter-denable software

Standard CLOSE- and OPEN-trigger circuits

Parameter-denable, adaptive control

Two switching procedures can be specied at the same time

Linear and vectorial compensation

Secure current measurement with Ring-type transducers

Software operation protected by user hierarchy

Evaluation using graphic user interface

RS 485 and RS 232 communication interfaces

Switching history can be transferred

Cyclic history, alarms, measurement values

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5Technical Data

Voltage supply:

Voltage: 40...360 Vdc Power consumption: 15 W Mains buffering, protected against polarity reversal, short-circuits, no-load and over-load, monitoring of supply interruption

Analog inputs:

1x temperature 4...20 mA, 24 V internal supply 3x oil pressure 4...20 mA, 24 V internal supply 3x reserve 4...20 mA, 24 V internal supply

1x control voltage 0...300 Vdc same reference dimensions, insulated 1x MAKE-trip voltage 0...300 Vdc same reference dimensions, insulated 1x OPEN-trip voltage 0...300 Vdc same reference dimensions, insulated

4x voltage transformer 0...212 Vac f0=1 kHz, Rin=240 k, insulated 3x current transformer 1,5,10 Arms f0=1 kHz, Rin=88 m, insulated, 100 A, 5 ms, Imax=100 A (5 ms) Digital inputs:

1x MODE 45...300 Vdc, Rin=20 k protected against polarity reversal, insulated 1x AUX-make-contact pole A 45...300 Vdc, Rin=20 k protected against polarity reversal, insulated 1x AUX-make-contact pole B 45...300 Vdc, Rin=20 k protected against polarity reversal, insulated 1x AUX-make-contact pole C 45...300 Vdc, Rin=20 k protected against polarity reversal, insulated 1x AUX-open-contact poles ABC 45...300 Vdc, Rin=20 k protected against polarity reversal, insulated 1x CLOSE-command 45...300 Vdc, Rin=20 k protected against polarity reversal, insulated 1x OPEN-command 45...300 Vdc, Rin=20 k protected against polarity reversal, insulated

3x Reference contact 4...20 mA, 24 V internal supply Outputs:

3x power outputs CLOSE 24...300 Vdc, 20 A, 2.5 s or 25 A, 200 ms (90C), 3x power outputs OPEN Imax=30 A (90C), short-circuit interrupt time

Please send me more information on the following topics:

High-voltage circuit-breakers for outdoor installation

High-voltage circuit-breakers: Type 3AP1/2, 72.5 kV to 420 kV

Live-tank and dead-tank high-voltage circuit-breakers technology

High-voltage circuit-breakers: Type 3AT2/3, 245 kV to 550 kV

Hydraulic operating mechanisms for high-voltage circuit-breakers

SF6 in power engineering acting responsibly

Further copies of this brochure

Siemens AGPower Transmission and DistributionHigh Voltage DivisionNonnendammallee 10413629 BerlinGermany

www.hv-circuit-breaker.comwww.siemens.com/ptd

The information in this document contains general descriptions of the technical options available, which do not always have to be present in individual cases. The required features should therefore be specied in each individual case at the time of closing the contract.

Subject to change without prior notice.

Order No. E50001-U113-A145-V2-7600 Printed in Germany Dispo 30000 By. PA 1105 1.5

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