Section 7 Control and monitoring

7.1.1 Control engineering systems are, in general, to comply with the requirements of Vol 2, Pt 9, Ch 7 Control, Alerts and Safety Systems.

7.2.1 An overspeed protective device is to be provided for main and auxiliary turbines to shut off the steam automatically and prevent the maximum designed speed being exceeded by more than 15 per cent.

7.2.2 Where two or more turbines of a compound main turbine installation are separately coupled to the same main gear wheel, and one overspeed protective device is provided, this is to be fitted to the L.P. ahead turbine. Hand trip gear for shutting off the steam in an emergency is to be provided at the manoeuvring platform.

7.3.1 Where a turbine installation incorporates a reverse gear, electric transmission or reversible propeller, a speed governor in addition to, or in combination with, the overspeed protective device is to be fitted, and is to be capable of controlling the speed of the unloaded turbine without bringing the overspeed protective device into action.

7.3.2 Auxiliary turbines intended for driving electric generators are to be fitted with speed governors which, with fixed setting, are to control the speed within 10 per cent momentary variation and 5 per cent permanent variation when full load is suddenly taken off or put on. The permanent speed variations of alternating current machines intended for parallel operations are to equalise within a tolerance of ± 0,5 per cent.

7.4.1 To provide a warning of excessive pressure to personnel in the vicinity of turbine exhaust ends, sentinel relief valves are to be provided at the exhaust ends or other approved positions of all main turbines, and the valve discharge outlets are to be visible and suitably guarded if necessary. Where a low vacuum cut-out device is provided, the sentinel relief valve at the L.P. exhaust may be omitted.

7.4.2 To provide a warning of excessive pressure to personnel in the vicinity of turbine exhaust ends, sentinel relief valves are to be provided at exhaust ends of all auxiliary turbines and the valve discharge outlets are to be visible and suitably guarded if necessary. Low vacuum or overpressure cut-out devices, as appropriate, also to be provided for auxiliary turbines not installed with their own condensers.

7.5.1 Where steam turbines for propulsion purposes are fitted with automatic or remote controls so that under normal operating conditions they do not require any manual intervention by operators, they are to be provided with the alarm and safety arrangements required by Vol 2, Pt 2, Ch 3, 7.5 Steam turbines for propulsion purposes 7.5.2 to Vol 2, Pt 2, Ch 3, 7.5 Steam turbines for propulsion purposes 7.5.7 and Table 3.7.1 Steam turbine machinery: Alarms and safeguards as appropriate. Alternative arrangements which provide equivalent safeguards will be considered.

7.5.2 Where a first stage alarm together with a second stage alarm and automatic shutdown of machinery are required by Table 3.7.1 Steam turbine machinery: Alarms and safeguards and Table 3.7.2 Steam turbine machinery: Additional alarms and safeguards, the sensors and circuits utilised for the second stage alarm and automatic shutdown are to be independent of those required for the first stage alarm.

7.5.3 Audible and visual alarms are to operate, and indication is to be given at the relevant control stations to stop or reduce the speed of the turbine(s) for the following fault conditions:

1. Excessive turbine vibration.

2. Excessive axial movement of turbine rotor.

3. Low vacuum in main condenser.

4. High condensate level in main condenser.

7.5.4 Reduction of speed may be effected by either manual or automatic control.

7.5.5 Means are to be provided to prevent the risk of thermal distortion of the turbines, by automatic steam spinning, when the shaft is stopped in the manoeuvring mode. An audible and visual alarm is to be provided at the relevant control stations when the shaft has been stopped for a predetermined time.

7.5.6 The following turbine services are to be fitted with automatic controls so as to maintain steady state conditions throughout the normal operating range of the propulsion turbine(s):

1. Lubricating oil supply temperature.

2. Condenser condensate level.

3. Gland steam pressure.

7.5.7 Prolonged running in a restricted speed range is to be prevented automatically or, alternatively, indication of restricted speed ranges is to be provided at each control station.

7.6.1 Where steam turbines for auxiliary purposes are fitted with automatic or remote controls so that under normal operating conditions they do not require any manual intervention by operators, they are to be provided with the alarm and safety arrangements required by Table 3.7.2 Steam turbine machinery: Additional alarms and safeguards as appropriate. Alternative arrangements which provide equivalent safeguards will be considered.