Woodward DECS-100-B15 Generator Voltage Regulator — Direct Retrofit Replacement for Legacy AVRs

Brand WOODWARD

Model Woodward DECS-100-B15

The Woodward DECS-100-B15 is a microprocessor-based Digital Automatic Voltage Regulator (AVR) and excitation control system designed to precisely regulate terminal voltage and manage reactive power on brushless synchronous generators. Originally developed under the Basler DECS-100 platform and now part of the Woodward generation control portfolio, the Woodward DECS-100-B15 consolidates voltage regulation, reactive power and power factor control, excitation limiting and protective functions into a single compact panel-mount controller. It is engineered for generator sets up to 5 MW across diesel, gas, turbine and hydro prime movers, serving as the critical interface between the generator’s exciter field and the plant’s voltage and VAR management strategy.

At its core, the Woodward DECS-100-B15 continuously measures generator terminal voltage and compares it against a configurable setpoint, then drives a PWM field output to the exciter to hold voltage within ±0.25% from no load to full load. The unit supports single- and three-phase potential transformer (PT) sensing across 100/120, 200/240, 400/480 and 600 VAC, accepts 1 A or 5 A CT inputs for reactive power and power factor calculations, and operates from an 88–264 VAC auxiliary supply — making it exceptionally flexible for both new installations and retrofit projects. Its value is most visible in applications where voltage quality, VAR sharing between paralleled machines and protection against excitation faults directly determine plant reliability and revenue.

The Woodward DECS-100-B15 is the “intelligence” of the excitation system: it not only keeps voltage steady under changing load, but also brings the generator online smoothly through voltage matching, prevents rotor and stator stress through layered excitation limits, and communicates operating data to the plant DCS or SCADA for monitoring and remote setpoint adjustment.

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Description

Technical Specifications

Parameter	Value
Product Model	DECS-100-B15
Manufacturer	Woodward Inc. (orig. Basler DECS-100 platform)
Product Type	Digital Automatic Voltage Regulator / Excitation Control System
Regulation Accuracy	±0.25% steady state, no load to full load
THD Performance	≤0.5% regulation accuracy at 40% total harmonic distortion
Auxiliary Supply	88–132 / 176–264 VAC auto-sensing, 50/60/400 Hz
Sensing Input	100/120, 200/240, 400/480, 600 VAC, single or three-phase
CT Input	1 A or 5 A secondary (B15 = 5 A CT configuration)
Field Output	0–63 VDC @ 7 A continuous, PWM
Forced Excitation	135 VDC @ 15 A for 10 seconds
Minimum Rotor Resistance	9 Ω
Control Modes	AVR, FCR (manual field current), VAR, PF, droop
V/Hz Limiting	0–3 per-unit adjustable
Communication	RS-232 (BESTCOMS), RS-485 Modbus RTU
Protection Functions	Overexcitation shutdown & limiting, underexcitation, overvoltage, loss of sensing, underfrequency
Operating Temperature	-40 °C to +70 °C
Enclosure Rating	IP20 (panel-mount module)
Approximate Dimensions	280 × 240 × 85 mm (panel-mount version)
Approximate Weight	3.5 kg
Compliance	CE, cULus (UL 508 / CSA C22.2 No.14), DNV, RoHS

Main Features and Advantages

The Woodward DECS-100-B15 stands out through the combination of measurement precision, operational flexibility and integrated protection. Its ±0.25% steady-state regulation accuracy, maintained even under 40% harmonic distortion, means clean, stable voltage for sensitive loads — a decisive advantage in data centers, offshore platforms and industrial plants where a few volts of deviation can trip downstream equipment.

The 63 VDC / 7 A continuous PWM field output, backed by a 135 VDC / 15 A ten-second forced excitation capability, gives the generator real authority during system disturbances. That short-term boost raises terminal voltage quickly when the grid needs it most, improving transient stability and reducing the risk of protective relay trips. A minimum rotor resistance of 9 Ω covers the vast majority of small to mid-size brushless exciters, so the Woodward DECS-100-B15 rarely requires external power stage add-ons.

Multi-mode control is where the unit proves its versatility. AVR mode holds terminal voltage for island operation; FCR (manual) mode lets operators control field current directly during commissioning or unusual conditions; VAR mode balances reactive load across paralleled generators; PF mode keeps power factor at a set target when connected to utility; and droop settings with cross-current compensation ensure smooth reactive sharing among multiple units. Integrated voltage matching automatically brings generator voltage into alignment with bus voltage before synchronizing, eliminating the voltage “bump” at closure.

Protection is layered and purposeful: overexcitation limiting and shutdown defend the rotor from thermal damage, underexcitation limiting prevents loss-of-synchronism, V/Hz limiting protects the core under low-frequency operation, and loss-of-sensing handling either trips or transfers gracefully to manual excitation rather than leaving the machine uncontrolled. A relay alarm output reports fault status to the DCS. Configuration through BESTCOMS PC software, front-panel Raise/Lower adjustment and LED status indicators make commissioning and troubleshooting straightforward even for sites without dedicated excitation engineers.