The rack provides backplane communication for interconnection among all racks of the Bently Nevada 3500 system and supplies required power to each module.
2.2 Power Supply Module
The power supply module of the 3500 system is a half-height module, which must be installed in the specially designed leftmost slot of the rack. One or two power supplies (AC or DC modules in any combination) can be fitted in a 3500 rack. Users can select any one of four types of power modules, and the upper and lower power units do not have to be identical. For instance, the upper one can adopt 220VAC while the lower one uses 24VDC.
2.3 Rack Interface Module (RIM)
As the basic interface of the 3500 rack, the Rack Interface Module supports Bently Nevada’s proprietary protocol for rack configuration and on-site unit data retrieval. It must be installed in the first slot right next to the power supply module.
2.4 Monitor, Relay and Communication Gateway Modules
In terms of hardware layout of the 3500 system, only power modules and rack interface modules are fixed to designated slots; all other modules can be mounted in any available slots inside the rack.
2.4.1 Monitor Module
The monitor module collects sensor signals on site, processes the acquired data, compares measured values with alarm setpoints, and transmits data from the monitor rack to rack interface modules, relay modules, communication modules and other peripheral systems. The 3500 system is equipped with a full range of monitor modules, among the most commonly used are keyphasor modules, eddy current / bearing vibration monitors, displacement monitors and speed monitors.
2.4.2 Relay Module
Relay modules output alarm signals transmitted from monitor modules. Main types include standard full-height 4-channel relay modules, redundant half-height 4-channel relay modules (3 signal paths per channel) and full-height 16-channel relay modules.
2.4.3 Communication Gateway Module
A communication gateway serves as a protocol converter, enabling data exchange between two systems with different communication protocols, data formats, languages or even architectures. It transmits selected status signals and current values digitally via Ethernet or serial communication to process control systems, historical data recorders, plant management computers and other relevant platforms. This module will not interfere with normal operation or mechanical protection functions of the 3500 system, ensuring full integrity of the monitoring system even in the rare event of gateway failure.
I. Software Configuration
3.1 Software Interface Introduction
Upon launching the 3500 Rack Configuration Software, users will see the interface shown in Figure 2-1 with the following sections from top to bottom:
Title Bar: Displays the full local storage path of the opened project file.
Menu Bar: Classifies all operational functions of the software for easy management and operation. The Tutorial option under the HELP menu provides systematic operation guidelines.
Shortcut Buttons & Rack Address: The rack address here is required for upper computer connection with 3500 instruments. For software versions above V3.90, an extra rack information button is added beside shortcut icons. It supports exporting rack data files including Alarm Event List, System Event List, Asset Information and Rack File for troubleshooting abnormal alarms and signal faults, or sending files to Bently Nevada for remote technical support. This operation is completed merely on the upper computer without affecting on-site rack operation.
Central Area: Used for configuration of all modules installed in the 3500 rack.
Status Bar at the Bottom: Indicates functions of left-click and right-click operations based on cursor position, offering practical hints for key operations.
3.2 Common Software Settings
3500 software configuration is straightforward, which mainly requires parameter matching with field devices. Below is the explanation of core configuration parameters for mainstream power plant modules including vibration, keyphasor, shaft displacement and relay cards.
Timed OK Channel Defeat: This function is permanently enabled for radial vibration channels. When sensor status recovers from abnormal to normal, it delays channel OK signal restoration for 30 seconds to avoid unit tripping caused by intermittent sensor faults. It explains why the OK indicator fails to light up immediately after wiring restoration during maintenance.
Direct Value: Represents peak-to-peak vibration values covering all frequency components within the specified frequency response range, corresponding to the full measuring span.
Gap: Refers to the physical distance between the eddy current probe tip and the measured metal surface, which can be displayed in displacement value or voltage value.
Clamp Value: Defines the fixed output value of the channel when it operates under abnormal status.
Alarm Delay: The delay time for Alert and Danger alarms of relative vibration is uniformly set to 3 seconds. Given that excessive shaft displacement may lead to thrust bearing abrasion and even catastrophic unit failure within seconds, the delay for high danger shaft displacement alarm is only 1 second. All delay parameters are configured independently inside each monitor channel, and relay modules execute Boolean logic based on delayed alarm signals.
Trip Multiply: This parameter is used to temporarily raise alarm thresholds, which is manually activated to allow units to pass high-vibration speed zones especially critical speeds without triggering alarms during startup. It is kept at 1 and not put into actual use in Ninghai Power Plant.
Probe Selection: Probes for bearing vibration measurement at No.1, 2 and 3 bearings must be high-temperature resistant models. Compressed air cooling is recommended if shaft seal tightness is unsatisfactory. Three high-temperature probes were burnt out in Ninghai Power Plant before cooling devices were installed. After confirming probe type, users can adjust sensor span factors. Since standard probes are adopted, OK limit is non-adjustable. The calibrated standard sensitivity is 7.874 mV/mm, equivalent to 200 mV/mil.
Alarm Mode: Divided into Latching and Non-latching modes. Latching mode keeps alarms active persistently even if measured values drop below set thresholds until manual reset is performed.
Sensor Direction Setting: The setting rule for displacement, velocity, acceleration sensors and keyphasor sensors is consistent, which is determined by the observation direction from the drive end towards the turbine tail end.
Keyphasor Signal Configuration: The signal trigger mode is set as Notch instead of lug type, and the sensor type is eddy current proximitor rather than electromagnetic sensor. Field device types can be confirmed via such configuration items.
II. Typical Fault Analysis
4.1 Indicator Light Status of Monitor Modules
Indicator light states cannot be modified via configuration, yet simple circuit disconnection faults can be judged by light flashing rules. The status rules of common 3500 monitor modules for vibration, differential expansion and shaft displacement are listed in Table 1 for quick fault diagnosis.
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