APPLICATION SPECIFIC FUNCTIONS
7-6. VIBRATION MEASUREMENT AND PROTECTION
Three different types of vibration sensors can be directly connected to the Mark V LM control panel. These sensors or transducers are mounted on several critical components of turbine and driven load to protect against long term excessive vibration damaging the turbine or load.
7-6.1. Seismic (Velocity) Sensors
Normally, there are three to five transducers on the turbine which generate a small ac current by passing a magnet through a fixed coil. The Mark V LM control processors interface directly with up to twelve vibration sensors or "pickups".
These sensors output a millivolt signal which is converted to a digital value proportional to vibration by I/O Configuration software on the TCQA board. The CSP in the <R> core uses this information in controlling and protecting the turbine. The seismic vibration pickups are terminated in the Mark V LM on the TBQB I/O Terminal board in location 7 on the <R2> and/or
The types of sensor diagnostic alarms provided include:
1. Open sensor detection and alarm. A small dc current is continuously passed through the vibration sensor at all times to detect a broken wire or other open input.
2. Shorted sensor detection and alarm. If the dc current is still flowing and there is no signal, a sensor short is alarmed.
3. Disabled sensor alarm. Failed sensors can be manually disabled via the operator interface and will result in a permanent alarm condition.
The vibration protection system will either trip or initiate a controlled shutdown of the turbine or generator under any one of the following conditions:
1. A shutdown will occur if several sensors fail or are manually disabled. (The number of sensors varies with each application, thus the number of sensors out of service before a shutdown occurs will vary.)
2. A trip will occur if a high level vibration is detected on any one sensor, 2a) and an adjacent pair of sensors is disabled or alarmed, 2b) or any other sensor is above the alarm limit.
2c) or two (2) or more sensor inputs are disabled.
Vibration inputs are monitored by the TCQA board which has a range of 0 to 0.75 V-peak and an input impedance of 100 to 2,000 ohms. Typical sensitivity ranges are 0.1 to 0.4 V peak-to-peak per inch per second.
7-6.1.1. CONFIGURING SEISMIC VIBRATION PICKUPS IN THE MARK V LM. The I/O Configurator on the operator interface configures the seismic vibration pickups. The TCQA seismic vibration screen is used to enable the input, disable diagnostic alarms associated with unused inputs, and to provide the I/O Configuration Constants for scaling. Additional I/O Configuration information for seismic vibration pickup diagnostic alarms are entered on a separate screen. The following fields are typically edited on the I/O Configurator screens:
Transducer-Used Field If a seismic vibration pickup is connected to an input point, the value YES must be entered into the Transducer-Used field on the screen and the sensitivity of the pickup must be entered in the corresponding Vibration Sensitivity field. If no pickup is connected to an input point, the value NO must be entered in the Transducer used field to prevent diagnostic alarms associated with the unused input point from being enunciated. If NO is entered under Transducer used, the value in the corresponding Vibration Sensitivity field is of no consequence.
Vibration Sensitivity Field The value entered in the Vibration Sensitivity field is the sensitivity rating of the velocity-type seismic vibration pickup, and must be in English engineering units (V/inch-per-second).
Seismic Vibration Transducer Open Circuit Field The entry in the Seismic Vibr. Xdcr. Open Ckt. field is the voltage above which a diagnostic alarm indicating a seismic vibration pickup open circuit condition exists (for all seismic vibration pickups). In order to accurately calculate this value, the pickup’s characteristics must be known, particularly the maximum expected resistance of the pickup circuit at maximum running ambient temperatures. The formulae for calculating the value will be displayed on the appropriate TCQA I/O Configurator screen
7-6.2. Accelerometer Inputs
Accelerometers are used to monitor vibration on aero-derivative gas turbines. The charge amplifiers, which are located on the turbine base, feed a velocity signal to the TBQE termination board. Three accelerometers can be monitored. Internal tracking filters are used to select the appropriate frequencies which result in alarm and trip protection of the turbine.
The Mark V LM is capable of both exciting accelerometer vibration sensors and scaling accelerometer feedback signals.
Configuring the Mark V LM to scale accelerometer input signals involves entering information on one I/O Configurator screen.
HP and LP rpm max scaling value Fields The entry in each of the three rpm maximum scaling value fields must be a power of 2 greater than the highest expected shaft speed for the high (HP) and low (LP) pressure shafts of the turbine when accelerometers are being connected to the Mark V LM. These entries are not related to the highest expected frequency from the shaft speed pickups, but the highest expected scaled shaft speed feedback signals.
7-6.3. Proximity Transducer Inputs
Proximity transducers use radio frequency waves to measure distance between an object and the probe. The transducer’s output is a voltage signal inversely proportional to this distance. The ac component of the transducer’s output is interpreted as vibration, while the dc component is interpreted as a change in position.
The Mark V LM provides a direct three wire interface to the proximity transducer for monitoring, alarm and trip. The number of probes that each Mark V LM has have the capability to interface with changes with the application, but typically values are:
• 8 vibration inputs
• 2 position inputs
• 1 key phasor inputs
Each proximity transducer receives -24 V dc power from the Mark V LM. The vibration inputs produce a dc voltage with an ac component which must be within 3 ac V peak-to-peak and -2 to -18 V dc. Each input terminates on a single termination point and is then internally wired with ribbon cables to the TCQE board in <R1>.
The input signals from proximity transducer (and associated key phasor) inputs will be wired to the TCQE board in <R1>. The first proximity transducer input points are designated for vibration sensor inputs (PRX01 – PRX08); the next two proximity transducer input points are designated for axial position/differential expansion sensor inputs; and the last proximity transducer input point is designated for a key phasor input. Several TCQE I/O Configurator screens are used to configure proximity transducer inputs, depending on the type of input signal (that is, vibration, axial position/differential expansion, or key phasor).
The following fields are typically edited on the I/O Configurator screens:
Proximitor Shaft Location Assignments Fields The TCQE I/O Configurator screen is used to set the shaft assignments for the proximity transducers. Valid entries for the field for each input are HP, LP and “--” (not used). For example:
the vibration proximity transducer input #1 is connected to a sensor mounted on a high-pressure turbine shaft bearing, therefore HP is entered in the field for the #1 input, meaning that the input signal will be filtered using the HP shaft speed.
Proximitors :- Peak to Peak Vibration Transducer Sensitivity Fields The vibration proximity transducers' nameplate sensitivity must be entered in the transducer sensitivity fields in order for the I/O Configuration software to scale the input voltage appropriately.
Proximitor low (or high) limit diag: Fields There are two fields in which voltage values corresponding to low and high limits for diagnostic alarms (indicating out-of-rage conditions) are entered. Common proximity transducers normally have an output range of -20.0 V dc to -2.0 V dc, with a typical voltage output of -10.0 V dc when properly installed and the shaft is at rest. Values in these fields will determine when the out of limits diagnostic alarm for the first eight proximity transducer inputs will be enunciated (these two values are for all of the first eight proximity transducer inputs).
Proximitors :- Position Inputs Transducer Sensitivity Fields Axial Position/Differential Expansion proximity transducer inputs are designated for use as either axial position or differential expansion inputs. The transducer's sensitivity, from the manufacturer's nameplate, must be entered in this field for each input point to which a transducer is connected in order for I/O Configuration software to scale the input voltage appropriately.
Proximitors :- Position Inputs Position Offset Fields The entries in the position offset fields will be dictated by the application. The offset setting is the zero position, at rest position, or starting position.
Proximitor low (or high) limit diag: Fields There are two fields in which voltage values corresponding to low and high limits for diagnostic alarms (indicating out-of-rage conditions) are entered. Common proximity transducers normally have an output range of -20.0 V dc to -2.0 V dc, with a typical voltage output of -10.0 V dc when properly installed and the shaft is at rest. Values in these fields will determine when the "out of limits" diagnostic alarm for proximity transducer inputs will be enunciated.
Proximitor Keyphasor Inputs Transducer Sensitivity Field Proximity transducer inputs are designated for use as keyphasor (shaft speed sensor) inputs. The transducer's sensitivity, from the manufacturer's nameplate, must be entered in this field for each input point to which a transducer is connected in order for I/O Configuration software to scale the input voltage appropriately and recognize the shaft's rotation indicator.
Proximitor Keyphasor Inputs Position Offset Field The entry in the position offset field for keyphasor inputs will be determined by field/Customer personnel as it must be the unit's desired offset in its zero speed condition.
Proximitor Keyphasor Inputs Low and High Diag: Field There are two fields in which voltage values corresponding to low and high limits for diagnostic alarms (indicating out-of-range conditions) are entered. Common proximity