Post on 03-Apr-2022
Control and Stability of Power System
Martin PistoraTechnical specialist
Trends in power industry in European context16th – 17th April 2014
Active power: How is it generated?
1. Steam pressure force acts on turbine blades2. This creates a torque (mechanical) turbine
moment Mt
3. Turbine is braked by an opposite (electrical) generator moment Me
For a steady state, the following equation can be written:
Relation between active power and frequency
Power factor– Defined as the active power change required for
the frequency change by 1 Hz– It relates to the robustness of the power system
K EPS = 800 MW/HzKCE = 26100 MW/Hz
Reactive power: How is it generated?By changing the excitation of synchronous machines
–Generators in the system–Synchronous condensers (now only at Substation Krasíkov)
Implementation of condensing elements– Chokes – Q– Capacitors – Q (there are no capacitors in the EPS system)
Lines depending on loads– P < Pnatural
– P > Pnatural
natural
Real-time control of P/f
Primary control / regulation (PR)– It makes frequency changes slower (Principle of solidarity)– It acts automatically within turbine governor– It can increase the deviation of power system
Secondary control / regulation (SR)– Activated remotely from the controller of EPS (LFC)– It controls the balance of power and frequency (Principle of
non-intervention)
Minute reserve capacity (MZt)– Activated manually by Quality Coordinator of EPS– It renews the control range of secondary control / regulation
Control of P/f – LFC diagramMeasured balance
Required balance
Actual hours
Manually
Required frequency
Measured frequency
Deviation
Correction
Output link from VE into PE input
Control of U/Q at the source
ARNARN • Reguluje nap tí
ípojnice
SRQSRQ • Reguluje Q generátoru
PRNPRN • Reguluje U generátoru
Qrequired
Uspecified
Substation
Power plant
It controls connection line voltage
It controls Q of the generator
It controls U of the generator
Sub-categories of stability
Dynamická stabilita
Dynamická stabilita
ÚhlováÚhlová Frekven níFrekven ní Nap ováNap ová
Dynamic stability
Frequency stability
Voltage stability
Angular stability
Angular stability
Ability of the machine to operate synchronously with the power system
It is influenced by:– Short-circuit capacity of the system,– Parameters of the generator.
Restoration of steady state after failure is influenced by:– Excitation of the generator (in particular),– Turbine control.
Angular stability
0
0.2
0.4
0.6
0.8
1
0 0.5 1 1.5 2 2.5 3
[pj]PM
[rad]
PE
Source: K. Máslo – Stability of ES, lecture for students of VUT Brno (Brno University of Technology)
a) single-pole scheme
b) substitute scheme c) vector diagram d) power output characteristic
Angular stability – weakening of the system
Source: K. Máslo - Stability of ES, lecture for students of VUT Brno (Brno University of Technology)
0
0.2
0.4
0.6
0.8
1
0 0.5 1 1.5 2 2.5 3
[pj]
PM
[rad]
PE
0 1
0
0.2
0.4
0.6
0.8
1
0 0.5 1 1.5 2 2.5 3
[pj]
PM
[rad]
PE
0
a) single-pole scheme
b) stable transition c) unstable transition
Angular stability – short-circuit fault
Source: K. Máslo - Stability of ES, lecture for students of VUT Brno (Brno University of Technology)
0
0.2
0.4
0.6
0.8
1
0 0.5 1 1.5 2 2.5 3
[pj]
PM
[rad]
PE0
0
PEZ
PE1
0
0.2
0.4
0.6
0.8
1
0 0.5 1 1.5 2 2.5 3
[pj]
PM
[rad]
PE0
0
PEZ
PE1
c) stable transition d) stable transition with quick valve control
a) short-circuit (line-to-earth) fault b) short-circuit switching-off
Frequency stability
Ability of the machine to maintain speed (frequency) close to the nominal value
It is influenced by:– Control range of the machine,– Parameters of TG set (inertia or persistence of the
machine).
Restoration of steady state after failure is influenced by:– Turbine control,– Response of load on frequency deviations.
Frequency stability
G
PM PE
Source: K. Máslo - Stability of ES, lecture for students of VUT Brno (Brno University of Technology)
Example: Starting-up of big TG sets
-5
0
5
10
15
20
25
30
0 100 200 300 400 500
Výko
n [M
W]
PG _EORL1 [ MW ] NT _EORL1 [ MW ]
Pow
er o
utpu
t [M
W]
Example: Starting-up of big TG sets
-2000
-1500
-1000
-500
0
500
1000
1500
2000
0 100 200 300 400 500
SG _EORL1 [ mHz]
Voltage stability
Ability of the system to transfer power output at given voltage
It is influenced by:– Short-circuit capacity of the system,– Parameters of the system.
Restoration of steady state after failure is influenced by:– Excitation set operation,– Load response.
Source: Z. Hruška - Calculations of voltage stability and coordination of voltage control, Internal workshop EPS 2010
Line transmission Load output
Substitution / normalization into p.u. [steady state operation?]
Final equation describing power transmission
Voltage stability
Voltage stability
Source: Z. Hruška - Calculations of voltage stability and coordination of voltage control, Internal workshop of EPS 2010
Persistence: Where can we see it?
Source: K. Máslo - Stability of ES, lecture for students of VUT Brno (Brno University of Technology)
Power failure 1500 MW
SummaryEPS controls (independently) under normal operation:– Voltage and reactive power,– Frequency and balance of transferred power output.
Dynamic stability can be divided into the following sub-categories:
– Angular stability,– Frequency stability,– Voltage stability.
Dynamic stability is strongly influenced by those characteristics which newly implemented power sources (with frequency converters) do not possess.