SYNCHROTACT® 5 Operating Instructions SYN 5201 SYN 5202

Functional principle 

2.1 Brief description 

The SYNCHROTACT 5 digital synchronizer is used for automatic synchronizing and 

paralleling of generators with lines and for the paralleling of already synchronous lines. 

The device is designed for system frequencies of either 50/60 Hz or 16 2

/3 Hz. 

SYN 5201 is a single-channel synchronizing device whose component choice and 

software design provides the highest security against incorrect paralleling. 

SYN 5202 consists of two independent channels with different hardware and software. 

This dual-channel property maximizes security against incorrect paralleling. 

All parameters required for paralleling are stored in a parameter set. The paralleling 

conditions and the characteristics of the voltage and frequency matchers are defined in 

this set. With the option providing seven parameter sets, paralleling can be carried out 

under different conditions or with different matcher characteristics using the same 

device. Seven configurable digital inputs and outputs are available for the selection and 

back indication of a parameter set. 

The data which are important for commissioning and for control purposes can be 

uploaded or downloaded using the PC tool SynView or, alternatively, via the keypad on 

Paralleling functions 

The automatic paralleling process can basically be divided into four function blocks: 

1. Measuring 

2. Voltage and frequency matching 

3. Monitoring of paralleling conditions 

4. Paralleling command generation 

In the following figure, the block circuit diagram of the basic paralleling functions of 

SYNCHROTACT 5 is simplified and shows a single-channel configuration. The 

individual functions are described more precisely in the following sections. 

Measuring 

The following measured variables are generated from the two single-phase measuring 

voltages: 

Voltage U1, U2 

U1 is the reference voltage e.g. line 

U2 is the adjustable voltage e.g. generator. 

Frequency f1, f2 

f1 is the reference frequency 

f2 is the adjustable frequency. 

Voltage difference ΔU 

ΔU = IU1I – IU2I 

ΔU > 0 Adjustable voltage is lower 

ΔU < 0 Adjustable voltage is higher 

Slip s 

%100*

1

21

f

ff s − =

s > 0 Adjustable frequency is less (e.g. generator is sub-synchronous) 

s < 0 Adjustable frequency is greater (e.g. generator is oversynchronous) 

Phase-angle difference α

α ϕ −= ϕ21

α > 0 Adjustable frequency is lagging 

α < 0 Adjustable frequency is leading 

Acceleration ds/dt 

dtds [ ]ss

x

x

x /%*2/

56

1

∑

=

=

Δ=

(Every 0.5 s, an average value is formed from 56 measurements; sampling period: 

9 ms) 

ds/dt > 0 Adjustable frequency is reduced (e.g. generator accelerates) 

ds/dt < 0 Adjustable frequency increases (e.g. generator is slowed down) 

With SYN 5202, the measurement is carried out separately for each channel. It is 

possible to carry out three-phase measurements in order to detect connection faults 

(rotary field, polarity) and losses of phase.

Voltage measurement (SYN 5202: channel 1) 

The two input voltages U1 and U2 are passed to the processor via high-impedance input 

resistors, differential amplifiers, low-pass filters and A/D converters. 

Voltage measurement channel 2 (SYN 5202 only) 

The two input voltages U1 and U2 are passed through high-impedance input resistors 

and differential amplifiers. The signal for the amplitude value is formed from this by 

conversion and filtering . For zero-passage detection, the signal is filtered and passed 

through a comparator. The signals prepared in this way are passed to the processor via 

the A/D converter

Voltage and frequency matching 

Working range of the voltage matcher 

If the voltage U1 is in the range between Umin and Umax and the voltage U2 is greater 

than U0max the adjusting commands are released. The direction of the adjusting 

commands depends on the polarity of ΔU. 

As an additional condition, both frequencies must be in the range fn±5 Hz. 

Voltage matcher with variable pulse times 

The voltage matcher issues a command the length of which is proportional to the current 

voltage difference. The proportionality factor dU/dt can be adapted to the voltage 

regulator. The voltage matcher aims at a value in the middle of the set tolerance band. 

The adjusting command length tp U is: 

dtdU

U U

U

tpU /

2

max max

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ Δ−−Δ+

−Δ

=

The adjusting pulse is discontinued as soon as the voltage difference passes through 

the target value. The command length does not fall below a settable minimum value. 

After an adjusting command, the system waits for the set pulse interval ts U so that the 

actual values can stabilise to the new setpoint. 

Voltage matching with variable intervals 

The function INVERSE U changes the way the voltage matcher functions. The pulses 

are now always the same length, but the intervals are inversely proportional to the 

voltage difference. 

Pulse length: adjustable by means of the parameter tp Umin: tp = tp Umin 

Pause interval: adjustable by means of the parameter ts U; dependent on ts U and 

±ΔUmax: 

[( ) ( )] 0

2

max max

*325,01* ≥

⎪⎭

⎪

⎬

⎫

⎪⎩

⎪

⎨

⎧

⎥

⎥

⎦

⎤

⎢

⎢

⎣

⎡ Δ−+Δ+ = −Δ−

U U

Utsts U

Voltage matcher for tap changer 

The function TAP CHANGER allows constant pulse durations and pulse intervals to be 

generated, which is necessary for matching by means of the tap changer. 

Frequency matcher with variable pulse durations 

The frequency matcher issues a command the length of which is proportional to the 

current slip. The proportionality factor df/dt can be adapted to the governor. The 

frequency matcher aims at a value midway between the nearer slip limit and zero. The 

adjusting command length tpf is: 

dtdf

s

s

tpf /

2

± max

−±

=

Between 1/3 and 2/3 of smax there is a range where no adjustment takes place. The 

adjusting pulse is discontinued as soon as the slip passes through zero. The command 

length does not fall below a settable minimum value. After an adjusting command, the 

system waits for the set pulse interval ts f so that the actual values can stabilise to the 

new setpoint. 

Frequency matcher with variable intervals 

The function INVERSE f changes the way the frequency matcher functions. The pulses 

are now always the same length, but the intervals are inversely proportional to the slip. 

Pulse length: adjustable by means of the parameter tp fmin: tp = tp fmin 

Pause interval: is calculated according to the following formula (can not be set as a 

parameter): 

[ ]s

sfff

ts 30

*1

1

21

1

≤= − =

2.2.3 Monitoring of paralleling conditions 

The monitoring of the paralleling conditions can be divided into these parallel-functioning 

blocks: 

• voltage-carrying lines 

• no-voltage lines 

Paralleling of two voltage-carrying lines 

The monitoring of the paralleling conditions enables a paralleling command (CHK 

RELEASE) if the following conditions are fulfilled simultaneously: 

• the phase-angle difference is within the tolerance band 

• the slip is within the tolerance band 

• the voltage difference is within the tolerance band 

• the voltage does not fall below minimum voltage 

• the maximum voltage is not exceeded 

• the device is in operating status (OPERATING) 

• nominal frequency deviation ≤ 5 Hz

Paralleling of no-voltage lines (dead bus) 

A special case for the monitoring is the paralleling of no-voltage lines. A paralleling 

command release is only issued if the external release signal is active and the 

measuring logic enables the release at the same time. The release by the measuring 

logic can be enabled if both voltages are within one of the permitted ranges. The dead 

bus range can be defined as permissible for one, the other or both measuring voltages 

by means of the parameters U1not, U2not and 1*2not.

The monitoring of the paralleling conditions (CHK RELEASE) releases the paralleling 

command if the following conditions are fulfilled simultaneously: 

• the releasing signal for dead bus (digital input) is issued 

• the zero voltage(s) does not exceed the set threshold U0max 

• the current voltage does not fall below the minimum voltage 

• the current voltage does not exceed the maximum voltage 

• the current zero voltage situation corresponds to a configuration permitted by means 

of U1not, U2not, 1*2not 

• the device is in Operating status (OPERATING) 

2.2.4 Command generation 

The command generation makes a distinction between asynchronous and synchronous 

sources or no-voltage lines. Two modes, one for asynchronous and one for synchronous 

sources, run in parallel, so that a source can be asynchronous or synchronous at any 

time. The paralleling command is issued in the mode in which all conditions are fulfilled 

first. 

In SYN 5202 the actuation of the paralleling relays takes place separately in both 

channels. 

Asynchronous sources 

It is called asynchronous sources, if the two lines to be paralleled (or generator and line) 

are asynchronous before the circuit breaker is closed. 

From the slip s, the acceleration ds/dt, the line frequency f1 and the set paralleling time 

t on, the command generation calculates the necessary lead angle αv by which the 

paralleling command is shifted forward in time so that the main contacts close exactly on 

phase coincidence (see following figure): 

⎥

⎦

⎤ ⎢

⎣

⎡ = + ont

ontdtds sfv *

2

*/

α *1*6,3

If the measured phase-angle difference α corresponds to the lead angle αv and if all 

paralleling conditions are fulfilled at the same time (CHK RELEASE), a command is 

generated (COMMAND). 

The command length always corresponds to the set paralleling command length tp on. If 

the latter is set to OFF or zero, the command generation is no longer in operation. The 

device then functions like a synchrocheck; as soon as the release is given by the 

monitoring (CHK RELEASE) the contacts close, when the release is dropped they open 

again.