STRATEGY AP2B TO REDUCE

LOAD SHEDDING IN DEFICIT CONDITION CASE : SOUTH SULAWESI

INTERCONNECTION Ricky Cahya Andrian

PLN AP2B Sistem Sulsel, PLN Wilayah Sulsel, Sultra dan Sulbar

Jln. Hertasning Blok B Panakukkang Makassar, Sulsel 90222

arrester97@yahoo.com

ABSTRACT- Load shedding in South Sulawesi Interconnection caused by insufficient reserves margin or (N-1) contingency if a large unit Bakaru 63MW out from the system. To minimize the load shedding, AP2B as a load dispatching and control system has a several strategy in order to control using Oil as fuel, controlling the voltage system with Brown Out to shed the capacitor or step down tap changer of transformator in Substation, load curtailment a big consumer Tonasa and Bosowa Cement and Captive Power 20kV in Hotel, Mall and the last load sheddingin residence. Keyword : deficit condition,load curtailment,load shedding, voltage control

I. INTRODUCTION

PT PLN (Persero) Wilayah Sulsel, Sultra dan Sulbar was divided into 9 distribution service area, 3 generation unit, Distribution Control Center (DCC) dan Load Dispatching and Controlling System (AP2B). South and West Sulawesi was divided into 7 distribution services area : Makassar, Bulukumba, Parepare, Pinrang, Mamuju, Palopo dan Bone. 2 generation unit : Bakaru area and Tello area, DCC and also AP2B. In addition in South East Sulawesi was divided into 2 distribution service area : Kendari and Baubau also 1 generation unit area Kendari.

The electrical system of South and West Sulawesi has been interconnected 150kV but in South East Sulawesi still have isolated 20kV system. The South

Sulawesi has 3 kind of voltage system 30kV, 70kV and 150kV. We have 28 substation and 2 big customer Bosowa (30MW) and Tonasa Cement (40MW).

A. GENERATION SYSTEM

Most of Electrical South and West Sulawesi system has been interconnected which 4 big plant unit as main support :

1. Sektor Bakaru, Bakaru Hydro Power Plant 117 MW

2. Sektor Tello, Diesel Power Plant Tello 197 MW

3. Diesel Power Plant Suppa 62.2 MW4. Combine Cycle Sengkang 135 MW

Several problems for generation system :

1. The capacity trend to go down was caused by no new plant was built and several unit have derating capacity. This matters cause the reliability to the customer being low comparing with several years before.

2. Hydrology condition (inflow) Bakaru Hydro Plant down drastically in October 2004, the same time Diesel Power Plant Suppa has crisis oil supply because from Pertamina.

This condition make thermal Tello run with high SFC (Spesific Fuel Consumption).

3. Thermal tello can’t be operated optimal in peak time because of its aging and has a high force outage number. GE unit as a peaking unit, still have several force outage problem.

The problems above has caused load shedding in South and West Sulawesi in planned and forced condition. Our system didn’t have a reserves margin anymore as well as Bakaru Hydro Plant 63MW or 15% from peak load 467MW.

B. LOAD SYSTEM

Customer in South Sulawesi was dominated by residence.Comparing among groups customer can be derived below :

TABLE 1.

Composition of customer PT PLN (Persero) Wilayah

Sulsel dan Sultra

NUMBER OF CUSTOMER GROUPS BASED TARIFF YEAR 2000 UNTIL MARCH 2005

Year

Social

Residence

Business

Industrial

Government

Amount

2000

17.756

1.168.336

39.525

1.192 6.210 1.233.019

2001

18.328

1.206.650

42.597

1.264 6.386 1.275.225

2002

18.927

1.233.050

44.623

1.287 6.656 1.304.543

2003

19.500

1.254.336

46.456

1.272 7.173 1.328.737

2004

20.163

1.269.618

48.368

1.229 7.978 1.347.356

until Mar05

20.344

1.276.264

49.135

1.221 8.165 1.355.129

AMOUNT OF CAPACITY (VA) PERGROUPS TARIFF YEAR 2000 UNTIL MARCH 2005

Year

Social

Residences

Business

Industrial

Government

Amount

2000

37.587.360

731.180.050

150.607.050

181.964.950

55.467.436

1.156.806.846

2001

39.774.960

780.919.55

165.087.95

185.046.48

55.836.438

1.226.665.38

0 0 5 32002

39.489.110

812.297.700

171.829.650

186.362.200

60.476.918

1.270.455.578

2003

42.488.760

838.599.850

189.147.173

195.344.050

65.531.112

1.331.110.945

2004

44.897.900

861.445.700

204.142.850

195.752.750

73.392.742

1.379.631.942

until Mar05

45.578.140

870.815.850

207.963.100

195.498.665

76.070.977

1.395.926.732

With great number for the residences groups, then using electricity more happened in the night. Industry which included in high voltage customer there were 2, Bosowa (30 MW)and Tonasa Cement (40 MW). This is why 2 customer here will more influenced more to the system condition.

The characteristic load for South Sulawesi System can be shown below :

Fig 1.Daily Load Curve and big customer

II. DISCUSSION AND SOLVING PROBLEM

A. OPERATION STRATEGY TO MINIMIZE LOAD SHEDDING

Facing the critical condition and didn’t have (N-1) contingency 63MW, will forced AP2B to do several strategies to minimize load shedding and the effect didn’t influenced the society and also still focused to the Oil Quota and cost operation.

KURVA BEBAN HARIAN

0

50

100

150

200

250

300

350

400

450

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 18 19 19 20 20 21 21 22 23 24

Jam

MW

Beban DasarTonasa BosowaTotal

1. Strategy Ordering Generation Unit

Strategy to order the generation unit in South Sulawesi System can be described :

1. In wet season : Hydro Power Plant as baseload. The main reason is cheap cost and the capacity 117MW can be used in baseload.

2. In dry season : Combine cycle as baseload. In dry season, capacity of Bakaru Hydro Power Plant cannot be maximized, so the other power plant to replace that hydroas baseload is Combine Cycle Sengkang. With the capacity 135MW, its cost operation isn’t expensive as Diesel Power Plant Suppa dan thermal plant in Tello. So, therefore in the morning time, we should reserve water which will be used for peaking time.

3. The operational priority of generation plant still based on Merrit Order. The lowest cost generation plant still in the highest top for operation,until the most expensive cost operation. The first place is Bakaru Hydro Power Plant (in normal inflow dan normal elevation), next Combined Cycle Sengkang, Diesel Suppa, Diesel Mitsubishi, SWD, GE, PLTU, Alstom dan Westcan. If the number of load shedding is high, then the expensive power plant can be operated but still focused on kuota Oil from the government.

2. Voltage Control Strategy

To minimize the number of load shedding, then we do the Brown Out (BO) to open capasitor in 70kV dan 20kV. For the opening capasitor 70kV can produce 2 MW per bank of capasitor. The number of capasitor bank 70kV are 6 banks di Tallo Lama Substation dan Daya Substation therefore total produce are 12 MW to the system. Then the capasitor 20kV can produce about 1 MW per bank. The number of capasitor bank 20kV are 6 banks in Sungguminasa Substation, Pangkep Substation and Tallo Lama Substation therefore can produce about 6 MW. Total are about 18 MW.

The other way for controlling the voltage 20kV is by stepdown the tap changer of transformer about 10% from the normal condition from 20kV into 19kV in substation inside the city dan 21kV into 20kV outside city. This strategy can produce about 8 MW in the off peak and 15MW on peak time to the system.

Total of these strategies are about 33MW in peak time.

3. Load Curtailment

Load curtailment is done for the biggest consumer in the system Bosowa and Tonasa Cement industry. Each of them about 10MW from the normal condition 40MW Bosowa and 30MW Tonasa. This matter is not easiest way, we need the compromise from both of them. The others, load curtailment also is done to the hotel and industry in Makassar area (Captive Power) for the 20kV system. This matter can produce about 18MW on peak time during 17.00 until 23.00. The total load curtailment are about 38MW on peak time.

4. Manual Load Shedding

Manual load shedding is the last strategy for outage schedule. The number of the outage is calculated after the above strategy done. And the number of the outage is delivered into several distribution area with proporsional number based on peak load of the distribution area. Load shedding started from outside substation then inner substation in the city based on scheduled in order to reduce the physicological effect to the residences. For VIP feeder will be priority not to open.

5. Automatic Load Shedding

Automatic Load Shedding will be working if there is forced outage on the generation plant off-scheduled (happened insidently) or fault in line transmission. The automatic load shedding is working based on relay UFR. For Sulsel interconnection system, 4 steps has been used from before only 3 steps.

Table 2.

UFR Relay in Sulsel

Priority Step

Frequency (Hz)

Load Shed (MW)

Cummulative (MW)

Step I 48.9 19.41 0Step II 48.7 27.38 46.79Step III 48.5 78.97 125.76Step IV 48.3 30 155.76

III. CONCLUSIONS

1. The outage in Sulsel System is caused by supply generation below than demands therefore we need

new generation plant so that reserves margin will have 15% or 1 biggest unit 63MW.

2. There are 5 strategy to minimize the outage or load shedding : generation plant strategy, voltage controlling, load curtailment, manual load shedding and automatic load shedding.

REFERENCES

[1] PEMBANGKITAN TENAGA LISTRIK, DJITENG MARSUDI

[2] RENCANA OPERASI SISTEM SULSEL