8.1.1  Test codes and practices - part 1

 

Condensing plant is the only major item of power plant which is at present not covered by a British Standard code for thermal performance testing.

For this reason, the CEGB has compiled its own test code, entitled 'Performance of surface-type steam condensers' — Site Test Code No. 3, 1981 [15].

Scope

This Code covers requirements for acceptance, routine and diagnostic testing of water-cooled surface-type steam condensing plant, including multi-pressure designs. It specifies procedures for testing condensers, and for calculating and reporting the results, so that the condenser performance may be checked against contractual obligations. In addition, the performance of different condensers may be readily compared, and the operational performance of condensing plant may be assessed.

Within this Code, reference is made in particular to the BEAMA design code [6] and to BS752: 1974 Test Code for Acceptance of Steam Turbines' [16].

General outline

The assessment as to whether a condenser meets its guaranteed performance is based on comparison of the condenser inlet pressure measured on the acceptance test (corrected to specified conditions of CW inlet temperature and flow, heat load, tube cleanliness and tube surface area) with the guaranteed condenser pressure.

When the test conditions differ from those specified, the Code describes a correction procedure which relies on validated curves or formulae and imposes close limits for permitted deviations when these are not available. The corrections are applied to the test logarithmic mean temperature difference (LMTD) and allowance is made for variation in steam temperature through the tubenest.

A method is also given for the routine assessment of condenser performance, in which the actual condenser inlet pressure is compared with that recorded during the acceptance test and corrected for the changes from acceptance test conditions to those obtaining at the time of the routine test.

A section dealing with test accuracy is included. The assessment of accuracy is based on the effect of systematic errors only, the random errors being effectively eliminated by the proposed frequency of readings.

Acceptance test procedures

Before testing, a meeting is held between all parties involved to discuss the testing programme, and to make arrangements for any necessary preliminary work. For example, discussions include reaching agreement with the manufacturer on:

  • Interpretation of contractual guarantees.
  • Location, type, and calibration of test instruments (Fig 4.33).
  • Means of obtaining the desired operating conditions.
  • Isolation of the plant for test purposes.
  • The procedures to be followed for calculating results.

By agreement, the official report of an acceptance test may be produced by either party to the test, or by representatives of the parties working together.

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