1.4 ETS SYSTEM MAINTENANCE
1.4.1 S YSTEM D ESCRIPTION
ETS (Emergency Trip System) which receives alarm signal or shut down signal from TSI system or other systems in turbo-generator set, does logic process, and outputs indicating lamp alarm signal or ETS signal. Redundant PLC are adopted to do logic processing for convenience and reliable operation. Two PLCs work
together. Any one of them can operate and output alarm signal. When one of the PLC is in trouble, it will send out fault alarm signal, and cut off shutdown logic output automatically. Another PLC works normally. The PLC can communicate with other systems to satisfy automation requirements of power plant.
The system includes a control cabinet; its internal logic is realized by ROCKWELL PLC (Dual PLC), which replaces the traditional relay, the logic hardware configuration:
PLC processor 1747-L542 Input module 1746-IB32 Output module 1746-OB32 PLC power supply 1746-P2 1.4.2 Working Principle
1.4.2.1 Two ETS PLCs work at the same time. Signal from site is sent to ETS device, and then delivered to PLC A and B at the same time. After automatic processing by internal logic, it sends out corresponding signal. Take “overspeed of turbine” as an example, when electric overspeed shutdown signal is sent to ETS, PLC A and B process and send out shutdown signal at the same time.
1.4.2.2 Any one of PLC A (B) is in trouble, it will send out alarm and disconnect shutdown output contacts automatically. Another PLC works normally. The work logic is shown in the following parts.
1.4.2.3 The ETS device is equipped with dual power sources switching loop. When one of the loops is in trouble, another will switch to work automatically. If two loops have trouble at the same time, the AC power supply loss signal is sent out. Two QUINT-PS power sources are redundant, and supply power (＋24V) to ETS device. ＋24V power loss signal is sent if this power source and PLC power source are in trouble.
1.4.2.4 Protection items of ETS
When any one of following conditions is activated, ETS system will send out TURBINE TRIP signal to DEH system to trip turbine.
1) Overspeed of turbine: when speed of turbine increases to 3300r/min and above, overspeed relay in overspeed monitoring channels of TSI activates.
Emergency trip signal is sent out by output interface after two out of three processing carried out in ETS;
2) Great axial displacement: when displacement between shaft of unit and thrust
bearing increases （≥1.2mm or ≤-1.65mm）, TSI sends out an emergency trip signal to ETS from a interface.
3) EH oil pressure is excessively low: when pressure of fire-resistant oil pipe
≤7.8MP, three pressure switches on fire-resistant oil pipe are closed. Three closed normally closed contacts send out emergency trip signal after two out of three processing done in ETS;
4) Lube oil pressure is low low: Set point of pressure switch is ≤0.1192MPa.
When pressure of lube oil pipe P≤0.0392MPa, three pressure switches (PSA4
～PSA6) in low lube oil pressure ETS device are closed. Three closed normally closed contacts send out emergency trip signal after two out of three processing done in ETS;
5) Vacuum of condenser is low: when pressure of condenser is ≥19.7KPa, three vacuum switches (PSB2 ～ PSB4) of low vacuum emergency trip device of condenser activate. Three closed normally opened contacts send out emergency trip signal after two out of three processing done in ETS;
6) Emergency shutdown of DEH: turbine emergency trip signal provided by DEH manufacturer.
7) Boiler emergency shutdown: digital signal from boiler is sent to ETS to trip turbine.
8) Generator emergency shutdown: digital signal from generator is sent to ETS to trip turbine.
9) Shutdown caused by over temperature of exhaust casing: digital signal from DCS is sent to ETS to trip turbine.
10) Shutdown caused by over temperature of metal of thrust bearing: digital signal from DCS is sent to ETS to trip turbine.
11) Manual shutdown: press manual shutdown button in central control room to shut down unit.
12) Excessive vibration of turbine: within 1# ～ 6# bearings, if any shaft bearings vibrates in X direction obviously （≥0.25mm） or within 1#～6# bearings, if any shaft vibrates in Y direction obviously （ ≥ 0.25mm ） , TSI outputs excessive vibration signal of shaft. The above logics are completed in TSI. TSI has an interface to connect with ETS to trip turbine.
1.4.3 Maintenance Items and Technical Requirements of ETS
1.4.3.1 Maintenance and calibration of primary elements
1.4.3.1.1 Lube oil pressure switch, condenser vacuum switch, and EH oil pressure switch should be calibrated according to calibration cycle.
1.4.3.1.2 Limit switch of main steam stop valve and interlocking valve should operate well and reliably. Lever should be fastened firmly. Polish contacts regularly.
1.4.3.1.3 Check secondary valves and blow-down valve carefully. The appearance of valve does not have serious corrosion. Valve plug moves easily, no oil leakage.
Connection of pipeline is in good condition, without leakage and blocking. After overhaul of pipeline, do blow-down till the pipeline is clean. Screws and hand-wheel should be complete.
1.4.3.1.4 Symbol should be correct and clear.
1.4.3.2 Maintenance and checking of protection loop
1.4.3.2.1 Check loops according to drawing. Make sure that connection wires are in good order and correct. Terminals are not loosening. Screws are tight and terminals are complete.
1.4.3.2.2 Use the megger to check insulation of cables. Insulation resistance between lines should be more than 20 MΩ and cable to grounding resistance should be more than 2MΩ.
1.4.3.2.3 Check signal channel and short connect protection contacts signal at site. Then, check and see whether PLC input signal lamp is on.
Notice: generally, the test is carried out before unit startup. If it is carried out during operation, corresponding protection measures should be taken.
1.4.3.3 ETS power source
When inspection, check whether main and auxiliary power sources are normal;
interference suppressor is installed to prevent interference signal at site from entering into control cabinet. Normally, inspect volt-meter of cabinet to see whether it indicates correctly.
1.4.3.4 Standby battery of PLC 1.4.3.4.1 Battery inspection
Service life of auxiliary battery of PLC is 5 years. When voltage of battery decreases to a certain degree, the alarm indication lamp on the panel will be on.
Replace the battery in time when battery alarm is found.
1.4.3.4.2 Procedures for replacing battery 1) Cut off power supply of PLC.
2) Remove cover. Take out old battery, and pull out the connector.
3) Install new battery connector within 30s.
4) Start PLC after putting the new battery.
1.4.3.5 Cabinet
Ensure that internal and external of cabinet are clean. All parts are complete and reliable. Design of fuse meets the requirements. Foundation of fuse is complete and clean, and leaf spring has a certain degree of elasticity. Clean connector by alcohol.
1.4.3.6 Relay
Appearance of the relay should be clean and trim, the pins are complete, and contacts are in good condition. Winding resistance should meet the requirements.
It can operate easily and reliable. Relay to grounding resistance should be more than 10 MΩ.
1.4.4 Test Prior to Unit Startup
ETS static test should be done before unit startup to ensure that software, hardware and protection of ETS system are correct and reliable. Except protection items, other protections switches in ETS cabinet have to be put to OFF before test.
Take turbine low lube oil pressure protection as an example.
1. Check if power supply of system is normal and if the test measures are complete.
2. Reset trip indication lamp on cabinet panel.
3. Short connect contacts of low lube oil pressure protection at site. Signal of indication lamps for alarm of low lube oil pressure and for shutdown are displayed on panel.
4. Corresponding indication lamp on PLC is on, and the corresponding relay activates.
5. Disconnect switch of low lube oil pressure protection. Reset alarm signal on panel.
6. Do next test.
1.4.5 Operation and Maintenance of ETS 1.4.5.1 Operation conditions of ETS
1) ETS and auxiliary equipment are all in good conditions.
2) Logical condition of ETS, alarm (beyond limitation) and protection activation setting points are accurate. System test is satisfied.
1.4.5.2 Maintenance of ETS
1) Check that if all protection items of ETS are put into service everyday.
2) check that if power supply of ETS system is normal everyday.
3) Check and make sure indication of indication lamp on ETS cabinet (panel) and indication lamp of PLC are normal. Check and see whether there is alarm (fault) everyday.
4) Check operation of local pressure switch everyday. Make sure that there is no leakage.
5) Clean the equipment weekly. Keep equipment and nameplates complete and clean.
6) Check external connection half year or before unit startup. Clean the connection terminals block, check that if terminals and screws are firm.
7) Check logic of ETS system and set point of alarm value half a year. Record the results.
1.4.6 Common Faults and Trouble-shooting of ETS
1.4.6.1 Operation wrongly caused by drift of set point of pressure switch
Solutions: 1. calibrate pressure switches regularly. 2. Check protection signal state during inspection. Release protection when abnormal situation occurs and solve the problems immediately.
1.4.6.2 During unit operation, closing feedback signals of main steam stop valve or
interlocking valve are sent by mistake.
Solutions: during operation: if closing feedback signals of main steam valve or interlocking valve are sent by mistake, inform operator to strength monitoring. Take necessary protection measures and check travel switch at site.
1.5 Element and Instrument for I&C Measurement
1.5.1 Instrument for Temperature Measurement
Temperature detecting element mainly means thermocouple and RTD.
Thermoelectric temperature detecting element uses thermoelectric characteristics to transform physical quantity of temperature into electric quantity or resistance and so on, then sends the electric quantity or resistance signals detected to display instrument or DCS system. The measured value is displayed as temperature value, which makes operator to observe and learn working condition of medium and guides operator to operate correctly.
1.5.1.1 Thermocouple
1.5.1.1.1 Measurement principle and composition
The thermocouple measurement principle bases on the following: two conductors (different compositions) are connected to a loop, if temperature at the two connection points is different, thermocurrent will be produced in the loop. Two conductors compose the two electrodes of the thermocouple. The more temperature difference at the two points, the bigger the thermocurrent (thermo emf) is. If one end is inserted into temperature measurement area (working end), and the other end is connected to measured instrument (free end or cold end), the instrument will display thermoelectric value. If instrument dial uses the relation of temperature---electric potential, showing the temperature value, i.e., the temperature value will be read out directly.
Thermo emf produced in thermocouple loop is composed by two parts: electric potential for working end and electric potential for free end. The graduation dial of thermocouple take free end temperature 0℃ as the standard. Thermoelectricity produced by thermocouple is only related with materials and temperature difference at two ends of thermocouple, not related with the length and diameter of thermocouple.
Thermocouple consists of temperature-sensing element, protection sleeve, wiring box, metal reinforce tube and so on. It should meet the following requirements:
1) Electric insulation of the two poles.
2) Prevent thermo electrode from damage of harmful substance.
3) Ensure good thermocontact between measuring end and measured object.
4) Ensure that thermocouple transmitter is installed on the measured object intensitively and rigidly.
Pacitan power plant uses armored industrial thermocouple (mainly nickel-chromium—nisiloy, nickel-chromium--nickel-alumin(i)um), category degree No. is K and E.
1.5.1.1.2 Maintenance items and standard 1) Maintenance items
(1) Clean wiring terminal board;
(2) Check insulation, electrode and wiring;
(3) Calibrate the thermocouple;
(4) Check the protection sleeve;
(5) Check compensating conductor;
2) Maintenance technological standard
(1) Materials of temperature-sensing element plug and main pipeline should be same. Provide the materials survey report to the plug on high pressure and temperature pipeline.
(2) Thermocouple wiring box on insulation pipeline should not be in the insulation layer;
(3) Correct and obvious nameplate should be on the temperature-sensing element. Wiring box, cover board, screw should be complete, wiring should be firm;
(4) Keep the good contact between the armored thermocouple which is used to measure temperature of metal surface and the surface of measured object;
(5) There should be no foreign matter in protective sleeve. Ensure the proper inserting length to measure the accurate temperature. For common sleeve, the inserting length should reach the central line of main pipeline. As for the protective sleeve which is used to measure temperature in pressure medium, take the leakage test under 1.25 times of working pressure. There should be no leakage within 1 minute;
(6) Electrode surface should be clean without cicatrices and cracks. Welding end should be smooth and firm without embitterment and mechanical damage;
(7) Temperature at the joint of compensation conductor and thermocouple should be less than 70℃. The polarity connection should be correct;
(8) When installing compensation conductor again, it should go through metal tube or soft tube. It is not allowable to keep a joint between conductors. The installation should not be in the high temperature area;
(9) Use the thermocouple after the calibration meets the requirements;
(10) Clean the site after the thermocouple installation.
1.5.1.1.3 Common fault and corrective action of thermocouple 1) Fault analysis:
(1) Thermo emf is less than the actual value;
a) Electric leakage inside the thermocouple;
b) Inconsistent thermocouple type and the instrument dial;
c) Damp thermocouple inside;
d) Short circuit of wiring terminal in thermocouple wiring box;
e) Short circuit of compensation conductor;
f) Damaged measurement end;
g) Opposite polarities of compensation conductor and thermoelectrode;
h) Improper installation position or heating length;
i) Too high in temperature of reference end;
(2) Thermo emf is more than the actual value:
a) Improper thermocouple type;
b) Inconsistent compensation conductor and thermocouple type;
c) Improper thermocouple installation method or inserting depth;
d) Loose wiring between compensation conductor and thermocouple.
(3) Unstable measuring instrument indication:
a) Poor contact between wiring terminal and thermoelectrode;
b) Intermittent grounding and short circuit of thermocouple;
c) Nearly broken thermoelectrode;
d) Infirm thermocouple installation causes the swinging;
e) Intermittent grounding and short circuit of compensation conductor.
Carefully check and analyze the above condition. Eliminate fault to ensure the equipment in safety operation.
1.5.1.2 RTD (Resistance Temperature Detector) 1.5.1.2.1 Measuring principles and components
RTD is generally composed by temperature-sensing elements (resistance elements), insulated conduits, protective sleeve, leading wires and wiring boxes.
The heating part (temperature-sensing elements) is made by winding double fine metal wires evenly around the framework of the insulated material. There are two-wire, three-wire and four-wire systems of wiring modes and the three-wire mode is more popular to be used.
The temperature-measuring principle of RTD: the resistance value of the conductor or semi-conductor changes as the temperature varies. When the temperature changes, the resistance value of the temperature-sensing element changes correspondingly, and the changing resistance value is used as a signal and inputted into the display instrument to measure or control the medium temperature.
Most of RTD used in Pacitan power plant are armored thermal resistors, and a few others are assembly thermal resistors. The chosen category degree of the platinum thermal resistors is Pt 100.
1.5.1.2.2 Maintenance items and routine maintenance
1) Inspection of the protective sleeve: the method and requirement are same with that of the thermocouple protective sleeve;
2) Check the porcelain pipes of the temperature-sensing elements are in good condition, and the resistance wire is not broken or corroded.
3) Check circuit Insulation resistor;
4) Calibrate thermal resistor;
5) Check the historical trend of the important measuring points in every shift.
Timely remove the protective measures once finding out temperature fluctuation;
6) Tighten and clean the wiring terminals regularly.
1.5.1.2.3 Common faults and analysis
1) The indicating value is lower than the actual value or the indicating value is unstable: there is water in the protective sleeve, there are sweepings, dust on the wiring box or the thermal resistor is short circuit.
2) The indicating value is infinitely high: the thermal resistor is short circuit.
3) The indicating value is the minimum one: the thermal resistor is short circuit and the display instrument wiring is wrong.
1.5.1.3 Bimetallic thermometer
The bimetallic thermometer is made up of two firmly combined metal pieces, and the expansion coefficients of which are different. The temperature-sensing elements of the bimetallic thermometer are wound into spiral shape; one end of the bimetallic thermometer is fixed while the other end is connected to the shaft of the indicator needle. When the temperature changes, due to the temperature influence on the bimetallic pieces, the curvature of the temperature-sensing elements will be changed and it will drive the indicator needles to rotate via the shaft and the temperature value will be displayed on the graduated plate.
Maintenance and daily service
a Clean up the bimetal thermometer;
b Inspection for the protection sleeve;
c Insulation resistance inspection for electric contact thermometer;
d Insulation resistance inspection for electric contact connecting circuit;
e Accuracy inspection for the indicating value 1.5.1.4 Temperature switch
The temperature controller is composed of shell, thermometer bulb, capillary connecting line, thermometer protection sleeve, fixed end adjusting button of set value and so on.
After the medium is filled into thermometer bulb, the temperature will increase, and the liquid inside thermometer bulb will expand and flows to the moveable section through the capillary tubes. Thus displacement will be caused to the moveable section, after the temperature reaches to the set point, the switch will be activated, and thus control and alarm signal will be sent out by external circuit.
1.5.1.4.1 Maintenance Installation:
Before installation, protection measures should be made to prevent damage due to corrosive air, strong variation ambient temperature, sun radiation and water penetration.
Adjustment:
1) For the fixed switch difference type controller, use the end button to adjust the set value. The set value could be upper switch value or lower switch value.
The corresponding switch value after adjustment is controlled by the fixed switch difference of this control switch.
2) For the adjustable switch difference type controller, firstly adjust the lower switch difference by the end button, and then use the switch difference adjusting button to adjust switch value. The upper switch value after
adjustment is the total value of lower switch value and switch difference value.
Move the set value adjusting button in a counter clockwise to make the upper and lower switch value move upward. By moving switch difference end button counter clockwise, only switch difference will increase.
3) Example:
1 Adjust requirement;
The lower switch value after adjustment should be 20℃;
Upper switch value should be 30℃;
Switch difference value should be 20℃.
2 Method: adjust the value setting end button keep the lower switch value is 20℃, and then adjust switch difference adjusting button to keep the switch difference value is 10℃.
1.5.1.4.2 Daily maintenance 1 Clean
2 Appearance inspections: there is no leakage on thermometer bulb and capillary tube.
3 Check the historical trend of the signals which sent into DCS system everyday. Make solutions if there are any faults.
1.5.1.5 Digital temperature indicator:
Digital temperature indicator: Digital temperature indicator transforms the non-linear signal from the temperature measuring components into temperature non-linear voltage signal after linearization. The voltage signal is converted through the A/D
Digital temperature indicator: Digital temperature indicator transforms the non-linear signal from the temperature measuring components into temperature non-linear voltage signal after linearization. The voltage signal is converted through the A/D