Thytronic SME2-IS - Monitoring and Control Functions; ALB Frequency (Automatic Load Balancer) Protection

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SME2-IS - Manual - 06 - 2021
FUNCTIONAL CHARACTERISTICS
4.5 MONITORING AND CONTROL FUNCTIONS
— ALB frequency (automatic load balancer) protection
Foreword
ALB (automatic load balancer) protection processes the following values:
• frequency [Hz];
• derivative of the frequency [Hz/s].
The introduction of the derivative of the frequency is motivated by the need to quickly deal with
situations caused by large power decits.
The protection has the following regulations:
• Block functions
• Filter functions (measurement means and times)
• EAC1 : 81U, 81O, 81R
• EAC2 : 81U, 81O, 81R
The frequency and frequency derivative values are measured for each phase voltage:
• UL1
• UL2
• UL3
Operating logic
The functions EACx (EAC1, EAC2):
• First maximum/minimum threshold (81O/81U) frequency f>/f<1a [fxa]
• Second maximum/minimum threshold (81O/81U) frequency f>/f<1b [fxb]
• Maximum frequency derivative threshold (81R) df>1 [dfx/dt]
can be blocked when one of the following thresholds is violated:
• Minimum voltage Ueac<
• Maximum voltage Ueac>
• Maximum unbalance ULS>
the reference value is the difference in absolute value of one of the phase voltages
|UL1|, |UL2|, |UL3 | and the mean of the three (|UL1|+|UL2|+|UL3|)/3
• Maximum frequency difference UG>
the reference value is the difference in absolute value of the phase frequencies max
(f1-f2, f2-f3, f3-f1)
• Maximum variation between consecutive periods UDT>
if T1 and T2 are the amplitudes of two consecutive periods, the reference value is given by their
difference DT=|T1-T2|
• Maximum active return power P->
the reference parameter is the active power input at the bar side, the function can be enabled/
disabled
With EACx enabled (no block) LEDs and relays can be associated for local and remote verication.
Increasing reliability
For more precise measurements and improved insensitivity to transients, the following settings can
be made:
• Number of semi-periods for the average of the frequencies
• Number of semi-periods for calculating the rst scale df/dt
• Number of semi-periods for calculating the second scale df/dt
• Number of semi-periods for calculating the third scale df/dt
• Number of averages for calculating the rst scale df/dt
• Number of averages for calculating the second scale df/dt
• Number of averages for calculating the third scale df/dt