Research Article
Power System Blackouts: Analysis and Simulation of August 9, 2004 Blackout in Jordan Power System
Department of Electrical Engineering, Faculty of Engineering, Mutah University, 61710 P.O. Box (81) Karak, Jordan
Modem society has come to depend on reliable electricity as an essential resource for national security; health and welfare; commmrications; finance; transportation; food and water supply; heating, cooling and lighting; computers and electronics; commercial enterprise and even entertairnnent. Providing reliable electricity is an enormously complex technical challenge, even on the most routine of days. It involves real-time assessment; control and coordination of electricity production at thousands of generators, moving electricity across an interconnected network of transmission lines and ultimately delivering the electricity to millions of customers by means of a distribution network (Makarov et al., 2005).
Maintaining reliability is a complex enterprise that requires trained and skilled operators, sophisticated computers and commmrications, careful planning and design. Large outages or blackouts are infrequent because responsible system owners and operators protect the bulk power system through layers of safety- equipments. In searching for the causes of the blackout, the investigation team usually looks back through the progression of sequential events, actions and inactions to identify the cause(s) of each event (Bialek, 2005).
World experience since the American blackout in 1965 has shown that if no well-organized control of modem power pools is taken into accmmt, the opportmrity of cascading faulty processes may result in blackout of extensive areas even at the presence of big reserves of power (Bihain et al., 2002).
In order to localize the source of failure and to prevent its cascading, a defense organized in consecutive echelons is to be adopted; the first is the automatic security of stability, the second is the automatic fault clearing of the asynchronous state and the third is the frequency load shedding. With these consecutive reactions, even in case of small reserves of generating and transmission capacities, the large failures with a long break of electric supply can be avoided (Avramenko, 2003).
This study describes the application of emergency automatics as a powerful mean for maintaining of power system survivability.
THE POWER SYSTEM MATHEMATICAL MODEL FOR THE CALCULATION OF LONG-TERM TRANNSIENT
During large system failures, such as those, which have taken place recently in power pools of America and Europe, the frequency variations caused by these failures have a significant duration due to the development of emergency processes (Stanton, 1972). Modem computers with ordinary programs allow analyzing these processes in big multi-machine systems for calculation of the transient stability by based on the individual dynamic equations for each mrit. However, the so-called infrequent model (IFM) is more adequate in this case, as it reduces the time of calculation (Grenier et oZ.. 2005). The theoretical backgrormd of this approach is based on considering the common motion of the rotors of the parallel operating machines as the characteristic of power system as a whole.
Summing the equations of motion of the individual machines, in which rotational moments are equal to power:
(1) |
Where, Mi = Tji · Pri is the constant of inertia of the system (MW.s)
Tji-The constant of inertia of the nnit in seconds, Pn-Rated power, |
Pri-Rated power, |
Pmi-Mechanical power of the turbine, |
Pei-Electric power of the generator, |
δi-Generator's rotor angle. |
If the average-load angle of system δs is taken as the characteristic of system motion as a whole:
(2) |
Then, Eq. 1 can be transformed into the following form:
(3) |
The individual angle can be presented as the sum of its deviation and the angle of system as follows:
(4) |
Substituting (4) into (1 ):
(5) |
From (5), It is clear that at Δδi≠0 (as case of symmetric radial circuit with load and disturbance in the center) all, δi=iden il angle δs, completely determines the system motion.
If insignificant deviations Δδi≠0 are fmmd, they can be neglected. However, it is possible for the calculation of system dynamics to apply Eq. 3 for describing the infrequent model (IFM) of system motion.
Angles δi determine the EMF angles of the synchronous generators used for the determination of a quasi-stationary electric state on each step of calculation. In traditional (for calculation of transient stability) model, which takes into accormt individual motion of rotors, calculation of electric state is carried out at fixed angles δi of EMF. However, in case of IFM, the situation is different, fixed EMF results (if the system is not strictly symmetric) in obtaining of various individual rmbalances (Pmi-Pei) and consequently, various increases in the frequency , which contradicts with the initial assumption of IFM regarding the equality of all frequencies, i.e. fi = iden = fs = δs,+ f0 To overcome this contradiction, it is necessary to execute iterative calculation of quasistationary state, in which EMF angles of generators are different; pulling them together into a point of swing, which fades and finally results in a stationary electric state. As condition of stationarity, the equality of accelerations δi = idem = δs is considered instead of Pm≠Pe:
(6) |
Where Pei which is a frmction of all angles δi of the synchronous machines working in parallel, enters in both of Eq. 3 and 6, (n is the number of generators), their joint iterative decision is necessary and it will result in the equality δi = δs.
DESCRIPTION OF JORDAN POWER SYSTEM BLACKOUT ON 9.08.2004
Pre-fault conditions before disturbance at 19:28:51 were characterized by the following parameters: Total load of the system was about 1270 1.1W, total generation was 1100 MW, imported power from Egypt (on Taba-Aqaba 400 kV cable) was 206 MW and exported power to Syria was 61.1W.
Jordan grid is a double-circuit, 400 kV overhead lines Aqaba-Amman South-Amman North-Deyr Ali (Syria) (with total length of 365 km) and 132 kV network. Aqaba Thermal Power Station (ATPS) has 5 units with total power generation of 650 1.1W; Hussein Thermal Power Station (HIPS) near Amman has 7 units with total power generation of 362 MW.
The main events of the accident were:
Time:
19:28:51.590:A trip signal is given to fast valve closing at turbines of ATPS as a result of fast decreasing of pressure in gas pipe line.19:29:00.473: All generators of Aqaba IPS are switched off from power system.
19:29:01.055: 400 kV cable line Taba-Aqaba is disconnected at Taba. The trip was caused by the action of distance protection, where the line fast overloading was identified as a remote fault on the system.
19:29:04.055:Trips of generators G1, G2, G3 ofEl Risha power station.
19:29:04.641: Trips of generators G4, G2, G7, G5, G6 of HTPS. Stage 1 load shedding at Jordan and Syria power
19:29:05.017: 400 kV line Amman North-Deyr Ali is disconnected at Amman North by the action of frequency emergency automatic.
Total load shed was about 600 MW and blackout of Jordan power system has taken plcae.
RECONSTRUCTION OF THE EVENTS
For digital simulation, the external connections to Egypt and Syria power systems were represented by their equivalent generation and load. Trips of generators and lines were taken according to real actions of relay protection during the accident.
Fig. 1: | The decreasing power of turbines at Aqaba TPS |
Fig. 2: | The mechanical, active and reactive power of unit No. 1 of Aqaba TPS |
Table 1: | Settings ofFLS |
Fig. 3: | The Active, Reactive Power Flows and Current of the Marine Cable Taba-Aqaba |
Fig. 4: | P, Q Locus for the marine cable Taba-Aqaba |
Start of digital simulation begins at0.1s before appearance of trip signal for unit No. 4 of Aqaba TPS.
Settings of Frequency Load Shedding (FLS) obtained from Dispatching Center ofJordan Power System (JPS) are given in Table 1:
The difference between calculated value of the load tripped by FLS (768 MW) and the real value (about 600 MW) confirms the effectiveness of this automatic.
Figure 1 and 2 show the mechanical and electrical power decreasing during the accedent.
Figure 3-5 show the power flows, P, Q locus and R, X locus for the cable ofTaba-Aqaba, which was tripped by the fast overloading of the line after tripping 5 units of Aqaba TPS with a power of 650 MW.
Fig. 5: | R, X locus for the cable Taba-Aqaba |
Fig. 6: | The active, reactive power flows and current ofthe lineNorthAmman-Deyr Ali |
Fig. 7: | The frequency and voltage at North Amman substation |
Figure 8 shows power flows on the line Amman North-Deyr Ali before it was tripped by the action of frequency emergency automatic. Figure 6-8 show the frequency curve for North Amman (Jordan) and for the equivalent node of Syria. The comparison of results of digital simulation with the records of fault parameters during the accident on 9.08.2004 has confirmed sufficient accuracy of simulation, as a base for investigation of new automatic means to prevent failures with enormous unacceptable damage.
Fig. 8: | The frequency, active load and active generation for the equivalent node of Syria |
THE PROPOSED E:MERGENCY AUTOMATIC TO PREVENTJPSBLACKOUT
The main feature of emergency automatic that is used to prevent failure with huge unacceptable damage is the admissibility of controllable (quantity and duration), decrease of the functioning level for the sake of achievement of the strategic purpose-preservations of electric supply for the most important consumers and the possibilities of fast restoration of electric supply. Practically, decrease of the functioning level of the Electrical Power System is expressed in emergency switching-off a part of consumers in an extreme situation. However, in some cases, similar to failure 9.08.2004 in JPS, emergency disturbance is so great, that ordinary FLS had no time to react properly and blackout of the whole of the system has taken piace.
9.08.2004 failure shows that the desire to use cheaper fuel on Aqaba TPS-gas instead of black oil-creates danger of emergency stoppage of all generators. It should be noted that, although all of the 5 units of the station were consistently tripped, but initial independent outage was one-pressure decrease in a gas pipeline, such probability should have been taken into account. This outage then imposed on some other outage-false action of the distance protection that has tripped the link with Egypt, which resulted in development of the failure down to full blackout ofJordan power system.
The structure of extemallinks of JPS which, carry out the function of emergency preservation, is such one, that loss Egypt connection to Aqaba TPS results to a sharp increase ofthe imported power on the connection with Syria power system.
Fig. 9: | The active and reactive power flows and em-rent North Amman-Deyr_Ali Connection. (The proposed emergency automatic) |
Fig. 10: | The frequency and voltage at North Amman Substation. (The proposed emergency automatic) |
Therefore, this can be used as a signal for emergency automatics, which at once will trip a part of load to prevent decrease of frequency below the allowable level.
The analysis of the grid of Jordan power system shows that by emergency switching-off 5 132 KV lines-Amman South-Abduon (2 circuits), Bayder-Abduon, Amman South-Ashrafia, HTPS-Abdali it is possible to trip total load of 175 MW. Simulation have shown, that such automatics, together with FLS stage, which has a setting of 49.1 Hz and trips 121 MW, provides fmin = 49.03 Hz (Fig. 10) at a disturbance similar to failure 9.08.2004 (Fig. 9).
• | In Jordan power system, there is a probability of two heavy outages-the full stoppage of Aqaba TPS and the false switching-off of the link with Egypt power system. As result, the frequency in Jordan power system (together with Syria power system) decreases below 49.0 Hz. Under frequency protection will disconnect Syria power system, which in turns result in blackout of Jordan power system. |
• | At the above-described distmbances, ordinary FLS with an action depending on the decrease of frequency cannot prevent the development of emergency process that results in blackout of Jordan power system. |
• | Using the emergency automatics, proposed in this work, will trip out part of the load on the basis of fast increasing of the imported power through the link with Syria power system and consequently, preventing the complete blackout of Jordan power system |
ACKNOEDGEMENTS
I would like to thank Dr. Ahmad Heyasat, the General Director of NEPCO who opened the way to have very useful discussions with the Qualified Engineers of NEPCO and to obtain the essential system data. My deep thanks to Prof. V. N. Avremenko for his valuable help and consultation.