Implementation of Hydrogenerator Overcurrent Protection with
Minimum Voltage Blockage Using Embedded Systems
PURCARU Dorina
1, GORDAN Ioan Mircea
2, PURCARU Anca
31 University of Craiova, Romania,
Department of Automation and Electronics, Faculty of Automation, Computers and Electronics, Decebal Blvd. No.107, 200440 Craiova, Romania, E-Mail: [email protected]
2 University of Oradea, Romania,
Department of Electrical Engineering, Faculty of Electrical Engineering and Information Technology, Universitatii Street, No.1, 410087 Oradea, Romania, E-Mail: [email protected]
3
VIG-IMPEX, Romania,
C. Brancoveanu Street, No.20, 200233 Craiova, Romania, E-Mail: [email protected]
Abstract – This paper presents a modern and efficient solution for the implementation of the hydrogenerator overcurrent protection with minimum voltage blockage. The digital equipment which implements this solution is organized around an embedded system and provides facilities for on-line monitoring of hydrogenerator electrical parameters and post-failure analysis. The protection implementation supposes parameter configuration, editing the logical function of the overcurrent protection with minimum voltage blockage, assignation of relays in the monitored process and setting time delays. The used digital equipment generates one recording at each protection triggering. The analysis of experimental results confirms the advantages of the presented solution for implementing this protection.
Keywords: embedded systems; data acquisition; protection function; variables; threshold values; software application.
I. INTRODUCTION
Recently, the work of many researchers is focused on power quality measurement, monitoring and analysis of electrical events in power systems and hydrogenerator protection [1,2,3,4,5,6,7]. The previous solution used for the hydrogenerator overcurrent protection with minimum voltage blockage implies equipment implemented using conventional technology. The disadvantages of this solution are the following:
1) the protection logical function, the threshold values and the timings could only be hardware implemented;
2) only protection status can be signaled; 3) only one relay can be ordered;
4) the equipment provides modest performances at very large overall size.
This paper presents a modern solution for implementing the hydrogenerator overcurrent protection
with minimum voltage blockage. The PC-05/104 digital equipment (organized around an embedded system) performs the implementation of several complex protection functions for the synchronous hydrogenerator including the above mentioned protection [8,9]. This digital equipment
can be local or remotely connected to an IBM-PC/AT compatible equipment for the protection configuration and parameter setting, on-line monitoring and visualization of the hydrogenerator functional regime and parameters, post-failure analysis of the recording after each protection triggering etc.;
provides high performances at small size;
is able to control the status of maximum 8 relays assigned to different protections.
This work presents an overview of the digital equipment for implementing hydrogenerator protection functions (hardware architecture and software design), the procedure which implements the overcurrent protection function with minimum voltage blockage and some experimental results.
II. OVERVIEW OF EQUIPMENT FOR IMPLEMENTING THE HYDROGENERATOR OVERCURRENT PROTECTION WITH MINIMUM
VOLTAGE BLOCKAGE
A. Hardware Architecture
The hydrogenerator overcurrent protection with minimum voltage blockage can be implemented with PC-05/104 digital equipment organized around an embedded system (PC/104 CPU). The PC-05/104 block diagram is presented in Fig.1. Seven other protections for synchronous hydrogenerators can be also implemented using the same equipment [7,8,9]. The hydrogenerator electrical parameters monitored with PC-05/104 are UR, US, UT voltages of the R, S, T phases,
phases, IH homopolar current and their frequency, active
power, reactive power etc. Four voltage transducers and four current transducers convert UR, US, UT, UH, IR, IS,
IT, IH in eight analog inputs of PC-05/104 (Fig. 1): U1,
U2, U3, U4, I1, I2, I3, I4. The digital equipment samples
these analog inputs, performs the data processing and decides the hydrogenerator status; it can order, if necessary, the hydrogenerator disconnecting. PC-05/104 generates a recording when a protection function is activated; in this way a post-failure analysis is possible after each event. The hardware architecture of PC-05/104 digital equipment is detailed in [8] and its main components are briefly presented in the following.
PC/104 CPU is an embedded system recommended for industrial automation and process control [8]. DIO&TIMER multifunctional interface for data acquisition is electrically and mechanically PC/104 compatible; it has 24 TTL compatible inputs/outputs and programmable timer. ADC 104XA includes an analog-to-digital converter (16 bits resolution and 10µs maximum conversion time) and a 16 channel analog multiplexer.
Two modules PC/104 Analog IN performs the signal conditioning and electrical isolation of eight
single-ended analog inputs marked with U1÷U4 and I1÷I4. PC/104 Digital IN performs the signal conditioning and electrical isolation of eight digital inputs (IN1÷IN8) which represent external conditions for PC-05/104 equipment. For example, IN1 monitors the status of power switch which disconnects the hydrogenerator. PC/104 Rel OUT is a digital output module which prepares eight digital signals (R1÷R8) for controlling the status of eight relays (Rel1÷Rel8) in the monitored process. These relays are assigned to implemented protections, to protection start-up and to secondary protection (DRRI). All signal conditioning modules from Fig. 1 are PC/104 compatible.
Local MMI consists in an extra-flat keyboard and an alphanumeric LCD. The user can change the working mode and the communication line using the keyboard. The sampled analog inputs, current status of the selected protection and status of the power switch of the monitored hydrogenerator can be displayed on the alphanumeric LCD.
Equipment status display is provided by Signaling module, and Self-testing module performs the fault signaling or absence of voltage signaling.
Fig. 1. Digital equipment for implementing complex protection functions – Block diagram.
Digital Equipment for Implementing Complex Protection Functions (PC-05/104)
LPT
COM1 GP0
PC/104 CPU
GP1COM2 INT
DIO & TIMER PB0-PB5
PB7 PA PC FB-232
Interface
RS-232 Isolation
Module
IBM-PC/AT Compatible Equipment
8 Digital outputs (R1 ÷ R8)
8 Digital inputs (IN1 ÷ IN8)
PC-07/104 Process
Server
17
Self-Testing Module Signaling
Module 5 3 3
3
PC/104 Rel OUT 8
PC/104 Digital IN 8
Fault or Absence of
Voltage Signaling
SIGNAL CONDITIONING
MODULES
3
SIGNAL CONDITIONING
MODULES
8
8
8 Single-ended Analog Inputs (U1,U2,U3,U4,I1,I2,I3,I4)
PC/104 Analog IN
ADC 104XA
8 4
PC/104 Analog IN
4 4
4 4
Local MMI Keyboard
(4x2 keys)
Alphanumeric LCD (2x16 characters)
FB-232 Interface allows the remote connection to PC-07/104 process server, and an electrical isolation module RS-232 compatible allows the local connection to an IBM-PC/AT compatible equipment. The connection of PC-05/104 to this equipment makes the protection configuration and parameter setting, on-line monitoring of the hydrogenerator functional parameters and post-failure analysis of the recording possible after each protection operation etc.
B. Software Design Aspects
Software applications are implemented at three levels: associated with the equipment for implementing complex protection functions, for the user local interface and for remotely monitoring. All these software applications are detailed in [9]. Only the software application for the first level is summary presented in this work.
The software application associated with the PC-05/104 equipment is designed and written in ANSI C programming language and implements several functions:
a) management of the data acquisition process; b) low-level calculations;
c) implementation of the communication protocol with the process server or an IBM-PC/AT compatible equipment.
This software application implies the general working mode and configuration working mode. Switching the operating mode and the communication line (local or remote) is performed from the PC-05/104 keyboard.
The general working mode allows the monitoring of hydrogenerator electrical parameters and status and provides commands for relays based on the threshold values previously set. Only the following information can be displayed on the alphanumeric LCD of PC-05/104 equipment:
rms values of analog inputs U1÷U4, I1÷I4;
phase shifts (related to U1) of U1÷U4, I1÷I4;
current status of the protection equipment: ACT – ready for triggering, DEM – in start-up status, DECLANSAT – triggered;
status (ON or OFF) of the power switch associated with the monitored hydrogenerator. Some useful information for the post-failure analysis of the event is stored in a Spy file: the triggered protections, the moment when each protection was triggered, and several status variables.
The software application for the user local interface runs only if the configuration working mode is selected.
III. IMPLEMENTATION OF HYDROGENERATOR OVERCURRENT PROTECTION WITH MINIMUM
VOLTAGE BLOCKAGE
The hydrogenerator protection implementation starts with the parameter configuration i.e. the threshold setting for the rms values of U1, U2, U3, U4, I1, I2, I3, I4
and their phase shifts. An example for parameter configuration is presented in Table 1 and Table 2. The threshold values occurr in logical functions of implemented protections. It should be noted that the thresholds setting is performed in accordance with hydrogenerator functioning conditions.
PC-05/104 must be connected to an IBM-PC/AT compatible equipment or to PC-07/104 process server for editing and visualization of the hydrogenerator protection function. The main operating window is shown in Fig. 2 for the hydrogenerator overcurrent protection with minimum voltage blockage (acronym PMAX). IN1(DRRI) is a digital input which monitors the status of power switch that disconnects the monitored hydrogenerator
TABLE 1. Threshold setting for currents.
Monitored parameter Threshold values Maximum 1 Maximum 2 Minimum for phase shift validation I1 RMS Value
(I1v)
5.0028 A 5.5011 A 0.2541 A
Phase shift (I1d)
94.6 deg 273.6 deg
I2 RMS Value (I2v)
5.0016 A 5.5008 A 0.3744 A
Phase shift (I2d)
271.1 deg 359.1 deg
I3 RMS Value (I3v)
5.0028 A 5.5011 A 0.2640 A
Phase shift (I3d)
0.0 deg 360.0 deg
I4 RMS Value (I4v)
39.8240 A 78.8272 A 2.4320 A
Phase shift (I4d)
0.0 deg 360.0 deg
TABLE 2. Threshold setting for voltages.
Monitored parameter Threshold values Minimum Maximum Minimum for phase shift validation
U1 RMS Value (U1v)
50.0609 V 72.0605 V 5.0432 V
Phase shift (U1d)
- -
U2 RMS Value (U2v)
50.1802 V 72.0202 V 5.0218 V
Phase shift (U2d)
0.0 deg 360.0 deg
U3 RMS Value (U3v)
50.0127 V 72.0375 V 5.0055 V
Phase shift (U3d)
0.0 deg 360.0 deg
U4 RMS Value (U4v)
0.0123 V 14.0343 V 5.0055 V
RMS Value (U1v)
Fig. 2. Editing and viewing the hydrogenerator overcurrent protection function with minimum voltage blockage.
The threshold values used in Fig. 2 have the meanings from Table 1 and Table 2. If the rms value of U1 is below its minimum threshold value, minU1v=1. If the rms value of I1 exceeds its maximum1 threshold value, max1I1v=1.
The PMAX protection causes the hydrogenerator disconnection if I1, I2 or I3 exceeds its maximum1 threshold value simultaneously with the decreasing of the corresponding voltage below its minimum threshold value. This reasoning leads to the following expression of the negative logical function for PMAX protection:
(
+) (
⋅ +)
⋅= minU1v max1I1v minU2v max1I2v
F
(
minU3v+max1I3v)
. (1)The bolded threshold values in Fig. 2 are those which arise in the selected term of the implemented negative logical function. When F=0, the start-up period begins for PMAX protection; as a result, Rel5
and Rel7 (assigned relays of PMAX protection) work after only 3 seconds.
IV. EXPERIMENTAL RESULTS
Fig. 3 and 4 contain experimental results before and during a event which causes the PMAX protection triggering. More electrical parameters are displayed in a user selected time interval; for example, this time interval is between the moments 5.8500s and 6.3900s in Fig. 3. The measurement moment (t=5985ms in Fig. 3) is selected by the user and marked with one horizontal line in each figure.
The experimental results, obtained using the PC-05/104 digital equipment for implementing the overcurrent protection function with minimum voltage blockage, can be grouped as follows.
• The waveforms of analog inputs (U1÷U4, I1÷I4) and the status of digital inputs (IN1÷IN8), digital outputs (R1÷R8) and logical functions (S1÷S5), during the selected time interval, are all displayed in the center of each figure.
Relay activation
Selected term (term1) of the logical function
of PMAX protection START-UP relay
PMAX protection is
selected DRRI relay
DRRI relay assignation
START-UP relay assignation Number of the selected protection Selected term of the
logical function
Negative logical function (F not)
is selected
START-UP period External
validation delay
DRRI disabled Delay for DRRI
PMAX protection relay assignation (Re15 and Rel7)
Editing / viewing logical functions for the protection implementation
Area with facilities for
editing the logical function
(F) of the implemented
protection
Negative logical function (F not) is
edited
Fig. 3. Experimental results before an event which causes the PMAX protection triggering.
Fig. 4. Experimental results during an event which causes the PMAX protection triggering.
Phasor diagram at the PMAX protection triggering moment (t=9210ms)
Phasor diagram of UR,US,UT,IR,IS,IT, at the measurement moment
(t=5985ms) Phase shifts related to U1, measured in clockwise
direction and computed at the measurement moment (t=5985ms), before the event
Total rms values of analog inputs U1÷U4, I1÷I4 at the measurement moment (t=5985ms)
• The phase shifts related to U1, measured in clockwise direction and computed at the measurement moment are displayed above the waveforms in each figure.
• The total rms values of analog inputs U1÷U4, I1÷I4 and the rms values of the first harmonic of these analog inputs at the measurement moment, are all displayed under the waveforms in each figure.
• The phasor diagram of UR, US, UT, IR, IS, IT, at the
measurement moment, is also depicted; the notations used are IR for I1, IS for I2, IT for I3, UR for U1, US for U2 and UT for U3.
After a comparative analysis of the Fig. 3 and 4 we conclude that
1) the rms values of I1, I2 and I3 are approximately equal before the event (at the measurement moment t=5985.000ms in Fig. 3): I1v=2.972A, I2v=2.968A, I3v=3.019A;
2) the rms value of I2 exceeds its maximum1threshold value (I2v=5.439A>5.0016A) during the event (at the measurement moment t=9210.000ms in Fig. 4); the minimum voltage condition (the decreasing of rms value of U2 below its minimum threshold value, U2v=39.6V<50.1802V) was previously achieved; 3) the approximately equal rms values of I1, I2 and I3
before the event can be also observed in the phasor diagram from Fig. 3 where IR=I1, IS=I2, IT=I3; 4) the important increase of the rms value of I2 at the
measurement moment during the event can be seen in the phasor diagram from Fig. 4 where IS=I2; 5) PMAX protection is triggered (Rel5 and Rel7 relays
work) at the triggering moment (t=9210ms in Fig. 4). All this information is very useful for the post-failure analysis of the event that caused the protection triggering.
V. CONCLUSIONS
A complete and accurate post-failure analysis of electrical events in power systems is possible only knowing the time evolution (before and during the event) of the characteristic electrical parameters (waveforms, rms values, phase shifts and phasor diagram of voltages and currents of the R, S, T phases), the status of more relays in the monitored process etc. The PC-05/104 equipment for implementing several hydrogenerator protections allows getting all this information.
The solution for implementing the hydrogenerator overcurrent protection with minimum voltage blockage, presented in this paper, has provided very good
performances and a lot of versatility at an accessible cost for solving a precise technical problem, despite not being the result of advanced research in the hydrogenerator protection field.
The PC-05/104 equipment utility and robustness are confirmed by the results obtained in more than ten hydropower stations in Romania, where it runs for more than five years.
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