HAZOP_GUIDE_BRITISH_STANDARD_IEC_61882_2001

The example will be presented in two sections

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: e purpose of this clause is to give a small example of a typical HAZOP study at the System Block Diagram level to illustrate some of the points in this standard. The example will be presented in two sections: Licensed Copy: Puan Ms. Norhayati, Petroliam Nasional Berhad 4397000, 01 October 2003, Uncontrolled Copy, (c) BSI – a brief description of the system and a block diagram; – sample HAZOP worksheets exploring some of the potential deviations, reported “by exception only” (see Table B.3). It should be noted that the design used in this example is of a system at a limited level of detail. The design and the sample HAZOP study worksheets are illustrative only and are not taken from a real system. They are included to show the process and are not claimed to be complete. B.3.1 B.3.1.1 The application System purpose The application concerns train-carried equipment for Automatic Train Protection (ATP). This is a function implemented on many Metro trains and some mainline trains. ATP monitors the speed of the train, compares that speed with the planned safe speed of the train and automatically initiates emergency braking if an overspeed condition is recognized. On all ATP systems there is equipment on both the train and track-side whereby information is transferred from the track-side to the train. There are many different ATP systems in existence, all differing in the detail of how they fulfil the basic requirement. B.3.1.2 System description On board the train there are one or more antennae which receive signals from the trackside equipment giving information on safe speeds or stopping points. This information goes through some processing before being passed to a Programmable Electronic System (PES). The other major input to the PES is from tachometers or other means of measuring the actual speed of the train. The major output of the PES is a signal to safety relays such as the one controlling the emergency brake. Figure B.2 gives a simple block diagram of this. TRAIN BODY BOGIE MOUNTED Emergency brake PES Tacho processing Antenna processing Tacho generators Signals from trackside Antennae IEC 454/01 Figure B.2 – Train-carried ATP equipment 38 83 83 © BSI 28 1002−80ISB © 1002−80 ISB August 2001 Licensed Copy: Puan Ms. Norhayati, Petroliam Nasional Berhad 4397000, 01 October 2003, Uncontrolled Copy, (c) BSI 6 8812 E I2:C100 © BSI 28 August 1002−80 ISB © 2001 Table B.3 – E xample HAZOP worksheet for automatic train protection system STUDY TITLE: A UTOMATIC TRAIN PROTECTION SYSTEM REFERENCE DRAWING No.: A TP BLOCK DIAGRAM SHEET: 1 o f 2 REVISION No.: 1 DATE: TEAM COMPOSITION: D J, JB, BA MEETING DATE: PART CONSIDERED: INPUT FROM TRACKSIDE EQUIPMENT DESIGN INTENT: TO PROVIDE SIGNAL TO PES VIA ANTENNAE GIVING INFORMATION ON SAFE SPEEDS AND STOPPING POINTS No. Element Characteristic Guide word Deviation Input signal Amplitude NO No signal detected 2 Input signal Amplitude MORE 3 Input signal Amplitude 4 Transmitter failure Consequences Safeguards Comments Actions required Action allocated to Considered in separate study of trackside equipment Review output from trackside equipment study DJ Greater than Transmitter design mounted too amplitude close to rail May damage equipment Checks to be carried out during installation Add check to installation procedure DJ LESS Smaller than Transmitter design mounted too far amplitude from rail Signal may be missed As above Add check to installation procedure DJ Input signal Frequency OTHER THAN Different frequency detected Incorrect value Currently none passed to processor Check if action is needed DJ to protect against this 5 Antennae Position OTHER THAN Antennae is Failure of in other than mountings the correct location Could hit track and be destroyed Ensure that cable will keep antennae clear of track JB 6 Antennae Voltage MORE Greater voltage than expected Antennae and other equipment become electrically live Check if there is any protection against this occurring DJ Pick up of a signal from adjacent track Antennae short to live rail Cable should provide secondary support – 77 – 1 Possible causes BS IEC 61882:2001 39 93 Licensed Copy: Puan Ms. Norhayati, Petroliam Nasional Berhad 4397000, 01 October 2003, Uncontrolled Copy, (c) BSI STUDY TITLE: A UTOMATIC TRAIN PROTECTION SYSTEM REFERENCE DRAWING No.: A TP BLOCK DIAGRAM SHEET: 2 o f 2 REVISION No.: 1 DATE: MEETING DATE: TEAM COMPOSITION: D J, JB, BA PART CONSIDERED: INPUT FROM TRACKSIDE EQUIPMENT DESIGN INTENT: TO PROVIDE DATA TO PES VIA ANTENNAE GIVING INFORMATION ON SAFE SPEEDS AND STOPPING POINTS No. Element 7 Antennae 8 Characteristic Deviation Possible causes Consequences Safeguards Comments Actions required Action allocated to Output signal OTHER THAN A different signal is transmitted Pick-up of stray Incorrect signal may be acted upon signals from adjacent cabling Ensure that there is adequate protection from cabling interference JB Tachometer Speed NO No speed is measured Sudden wheel lock May show zero speed Check protection against this DJ 9 Tachometer Speed OTHER THAN Other than correct speed is detected Sudden release of locked wheels gives confusing signal May show wrong speed Check protection against this BA 10 Tachometer Speed AS WELL AS Many speeds indicated Sudden changes in output caused by wheel spin May cause action based on wrong speed Check if this is a problem in practice BA 11 Tachometer Output voltage NO No output Axles locked May show zero speed Check imp...
View Full Document

This note was uploaded on 09/15/2011 for the course ECON 102 taught by Professor Calvin during the Winter '11 term at Oxford Brookes.

Ask a homework question - tutors are online