1. Introduction
The commercial and technical conditions are all specified in the purchasing contract. It is commonplace for utilities to make special requests in order to assure the quality of the transformers fulfil the contract requirements. This step is also important in that the utility must manage the delivery of the transformers as it can delay the installation plans. This step is also important for the utility to manage the delivery time of the transformers to avoid the delaying installation plans such as to install the transformers before the contract can be completely settled to reach both the utilities and supplier’ satisfaction.
The contract acceptance is difficult when the delivered transformers do not conform to the contract specification which has many classifications such as: physical characteristic, exceeding the guaranteed loss, etc. It is the intention of this chapter to guide the utilities to learn and share experiences in solving these problems by sample analysis and conclusion.
2. Objective
Experience shows that there are three main factors to discuss in the process of transformer contract acceptance. One is a detailed specification with approval drawings, the second is routine test reports with guaranteed loss verification and the third is the final sampling test of the transformers before energizing and put in service. Various scenarios are given and explained to be used as a problem solving guide. It shows the process from top management’s policy viewpoint regarding practical standards in the procurement system.
3. Acceptance Committee Management
This follows the same procedure as mentioned above in the production inspection committee. The acceptance committees should be approved by upper management after the contract is signed. The acceptance committee members who cover the
technical information will be selected from the related department which is knowledgeable about transformer specification and testing at a minimum, as follows:
i. Research and development department which takes care of the transformer failure analysis
ii. Distribution equipment department which maintains records of the transformer’s data characteristic and performance evaluation.
iii. Testing division which has experience in transformer testing procedures.
iv. Purchasing or Contract department which controls the relevant documentation starting from the quotation, technical and commercial condition agreement and the approval drawings.
All engineers and technicians who are represented as the contract acceptance committee will be given the approval drawings as shown in Figure 12: List of approval drawings and related accessories for their reference during sampling of the delivered transformers for testing. Samples of technical and guaranteed data of the transformer are shown in Figure 13. The supplier shall submit the routine test report of all the transformers together with the transformers apart from the commercial document.
In the event of disagreement or dispute, either the contract’s details are not clear or the supplier would like that an exception be made (for example, the value of the guaranteed loss) these issues should be presented at a meeting with the upper management. The meeting should discuss the disadvantages and advantages to the utility as the main focus. This convention should remain and be considered the standard practice.
4. Acceptance Process
The acceptance committee will make a visual inspection for the quantity of the delivered transformers according to the invoice of the supplier, after scrutinizing all transformers and documents such as the instruction manual, spare parts, etc. The acceptance committee will then randomly select a quantity of transformers per that which is stated in the contract. This amount typically does not exceed 10 sets due to the expense and time.
It is recommended that even though the supplier performs the entire routine test for all transformers as shown in Figure 14: Supplier’s routine test report, the utility should perform sampling for its own re-verification before installation on site. The utility should implement a detailed step by step, pre-verification laboratory in order to assure that the transformers conform to the specification, especially with respect to guaranteed losses; otherwise, the supplier may try to deliver cheap transformers with high losses.
In the event that the utility has budgetary constraints, it is strongly recommended
that a third party be employed to witness the tests and approve all contract documents at the factory. This may require a monetary investment, but the value outweighs the cost due to the high cost of equipment.
At a minimum, the following acceptance tests should be done at the utility’s laboratory:
4.1. Routine Test
• Insulation Resistance Test
• Winding Resistance Measurement
• Oil Dielectric Test
• Applied Voltage Test
• Induced Voltage Test
• Ratio And Vector Group Test
• No-load Loss Test
• Load Loss Test 4.2. Type Test
• Temperature Rise Test - The sample of the utility’s acceptance test report is shown in Figure 15: Acceptance routine test report: as can be seen, the no-load loss and load loss are measured and calculated to verify that the sampling transformers’ losses conform to the guarantee values per the contract. The payment shall then occur and the file will close and include a guarantee of performance for one year after delivery.
4.3. Excess Loss Management
4.3.1. Case No. 1 - Utility randomly selects some transformers to compare with the supplier’s report.
i. If the utility’s values are greater than the supplier’s report by 2.5%, the utility will increase the supplier’s values of all transformers with the following consecutive procedures.
ii. The utility has to investigate which transformer’s values exceed the guaranteed values including the tolerance limits, the transformer(s) should be rejected and the remainder are considered for penalty by calculating the average values of the total number of transformers.
iii. The compensation penalty is calculated by using penalty values which are 2.0 times of the formula constants x values of loss exceeding x Total number of transformers, as shown in Figure 16 Penalty Calculation Without Raising the Guarantee Values.
iv. Some suppliers may ask the utility to accept the rejected transformer(s) considering clause 3 above, provided the average value of that transformer is:
• Guarantee load loss = 5,600 W
• The different average value between the utility and supplier = 5.61%
• Average supplier’s report value = 5,481.33 W
• New guarantee load loss is raised to = 5,481x1.0561 = 5,788.83 W
• The penalty is calculated to = (5,788.83 – 5,600)x penalty values (normally is 2.0 times of the formula constant) x Total number of transformers
This is illustrated in Figure 17 Penalty Calculation with Raising the Guarantee Values
4.3.2. Case No. 2 - Utility does not have the requisite facility for making acceptance tests and is dependent on the routine test report of all transformers in computing excess losses. The process will be the same as mentioned in case no. 1 above, by using tolerance limit instead of the different values between the utility and supplier.
i. In case of increased no-load loss, provided the supplier’s routine test report shows the following values:
• Guarantee no-load loss = 5,000 kW.
• Tolerance limit specified in the contract = 15 %
• Supplier report shows no-load loss = 6,000 kW > 5,000+15
%
• Increased no-load loss guarantee = 6,000/1.15 = 5,217.39 kW
• The penalty is calculated to = (5,217.39 – 5,000) x penalty values (normally is 2.0 times of the formula constant) x Total number of transformers
ii. In case of total loss exceeds the tolerance but with no-load loss within the limit, the increase in load loss to the new guarantee value is equal to (total loss)/( 1+%tolerance/100) – no-load as shown below:
• Guarantee no-load loss = 5,000 kW
• Guarantee load loss = 10,000 kW
• Tolerance of no-load loss = 15 %
• Tolerance of total loss = 10 %
• Supplier report shows no-load loss = 4,500 kW < 5,000 kW
• Supplier report shows load loss = 13,000 kW
• Supplier report shows total loss = 13,000+5,000 = 18,000 >
(5,000+10,000)+10% kW
• Raised load loss guarantee = (18,000/1.10) – 5,000 = 11,363.64 kW
• The penalty is calculated to = (11,363.64 – 10,000) x penalty values (normally is 2.0 times of the formula constant) x Total number of transformers
• Check again if the average supplier’s load loss is lower than the new guaranteed load loss value
NO.
1 OUTLINE DRAWING Tr. 6300 kVA, 3 Ph. Dyn 11 11000 - 6900/3984 V.
TYPE : CONSERVATOR
2 TRANSFORMER BASE
3 CABLE BOX TYPE 1
4 HV. LV. BUSHING WITH EXTENSION BAR
5 NAMEPLATE WITH CONNECTION DIAGRAM CONNECTION Dyn11
6 NAMEPLATE BUSHING CURRENT TRANSFORMER SPECIFICATION
7 NAMEPLATE TAG. NO.
8 CONTROL BOX
9 WIRING DIAGRAM OF INSTRUMENT
NO.
1 HIGH AND LOW VOLTAGE BUSHING DT 10 Nf 630 DIN 42532
2 HV. TERMINAL CONNECTOR 630 A.
3 LV. TERMINAL CONNECTOR 630 A.
4 OIL LEVEL INDICATION SO-HE-6
5 LIQUID FILLED THERMOMETER 1187/S
6 TAP CHANGER NO. 3
7 DEHYDRATING BREATHER SILICAGEL SIZE 3 KG.
8 GROUNDING PAD For cable 50 sq.mm.
GLOBE VALVE, oil sampling and drain valve
9 Upper filter valve
Oil sampling valve 1/2"
10 BUTTERFLY VALVE FOR RADIATOR FIN EE-W80
11 BUTTERFLY VALVE (For buchholz relay) DN 50
12 PRESSURE RELIEF DEVICE WITH CONTACTS COMEM/80T
13 BUCHHOLZ RELAY BR50
14 WINDING TEMPERATURE INDICATOR Messko (MT-ST160W)
15 RUBBER AIR CELL AIR CELL
NAME TITLE EFF. DATE : NAM E OF M ANUFACTURER 4
14
Figure 12: List of approval drawings
kVA FREQUENCY Hz.
N AME OF MAN UFACTURER REV.
Tr. 6300 kVA, 3 Ph. Dyn11 In order to keep the product's delivery schedule,
IEEE C57.12.00
please return the approval drawing before ………