Download - DC Current Measurement
Rotor DC Current Measurement by Using Current Transformers
Authors:Z. Gajić, ABB SwedenD. Trišić, Drinsko-Limske HE, SerbiaS.Roxenborg, ABB Sweden
Presented by Roger Hedding
Objectives
Information about typical excitation systems
Static excitation What is the role of an excitation
system New measurement principle for
rotor DC current Information about the trial
installation Show some captured recordings DC current use for the protection Conclusions
Power Station
CONTROL ROOM
CONTROL SYSTEMS
STEP UP TRANSFORMER
HV SYSTEM
STARPOINTCUBICLE
HV- SUBSTATION
TURBINEGOVERNOR
STATIC STARTER
SYNCHRONIZATION
1
1
Power Island
GEXCITATIONTRANS-FORMERTURBINE
MV SWITCHGEAR
PT’sCT’sSA’s
AUXILIARYTRANS-FORMER
MVDRIVES
LV SWITCHGEAR
EXCITATION SYSTEM
UNITPROTECTION
Two main types of excitation system
AVR
Regulation & Control Electronics
Excitation transformer
Converter
De-excitation
DC-breaker*
Field flashing
AC-breaker*
*AC- or DC breaker
Main Components Static Excitation Systems
Static Excitation System “Inside View”
ULVPh-Ph
Thyristor Controlled Rectifier
Note that phases are marked with letters R, S, T instead of A, B, C
Static excitation System
AVR
Excitation Transformer
Converter
ACCB
PT
CTController
Field Discharge
Provide variable DC current with short time overload capability
Control terminal voltage with suitable accuracy
Ensure stable operation with network and / or other machines
Contribute to transient stability subsequent to a fault
Communicate with the power plant control system
Keep machine within allowed operating range on P-Q diagram
HPP Bajina Bašta (Low Lake)
View of RHE from the dam
HPP Bajina Bašta (Upper Lake)
Overall Single Line Diagram of the Plant
315MVA11kV
100MVA15,75kV
0,2km 220kV OHL
Hydro Power Plant
220kV S/S Zaugline
8km, 220kV OHL (4 off)
Generator/Pump Unit Data
Turbine Francis 428.6rpm
Synchronous Machine 315MW pf=0.95 11kV; 50Hz
Unit Transformer 2*160MVA 242kV/11kV Yd5
Special Things about this Installation
Operating Modes Generator Motor (Pump) Electrical braking Synchronous start
(i.e. Back-to-Back)
Single Line Diagram of Machine Used in Trial Installation
Excitation System Three-Line-Diagram
Traditional Possibilities to measure DC current
Resistive Shunt Hall-effect sensor
Typically not possible to be used by the numerical protection relays
Primary connections
Connections to transducer
Required CT Connections for DC Current Measurement
100/5
1500/5
1400kVA11kV/0,55kV
Yd1
How the DC Current is Calculated ?
When HV CTs are used: IA, IB, IC are measured By using properties of
excitation transformer re-calculate Ia, Ib, Ic first
Then use formulas to the right
When LV CTs are used: Ia, Ib, Ic are measured Calculate instantaneous
DC current by using the following formula:
Calculate equivalent RMS value of the DC current by using the following formula:
Recordings from the Trial Installation
100/5
1500/5
1400kVA11kV/0,55kV
Yd1
IR_HV, IS_HV, IT_HV
IR_LV, IS_LV, IT_LV
HV_DC_I
LV_DC_I
R, S, T <=> A, B, C
Filed Record No 1
Filed Record No 2
Filed Record No 3
Filed Record No 4
Filed Record No 5
DC Current Value on the built-in HMI, via Comms, etc.
Conclusion
Patented DC current measurement in the numerical IED will improve the synchronous generator protection and monitoring.
Current based protection for the rotor winding can be done in an easy way (e.g. thermal overload).
Possible to record and monitor the rotor winding DC current together with Stator U and I in the same COMTRADE file!
Practical Advise
When more than one power source is used for the excitation equipment supply, use the CT located just in front of the six-pulse rectifier bridge in order to measure DC current under all operating conditions of the machine
5
2
3
6
4
1
7
89
220kV Transmission Network
Questions
Recording from Another Machine
8 10 12 1440-
20-
0
20
40 IAIBIC
W1 Current Waveforms
Time [cycles]
Cur
rent
[Am
ps P
rimar
y]
8 10 12 14
200
400
600
800HV_side
DC Current Integrated Value
Time [cycles]
DC
Cur
rent
[Am
pere
s]