GE Multilin D20, D400 and G500 RTU and Gateway

Short answer

The GE Vernova Multilin D20 (D20MX, D20/200ME) and D400 were for years the RTUs and gateways of many substations: they concentrate data from relays and meters and deliver it to the control center over DNP3, IEC 60870-5-101/104 or Modbus. GE Vernova now lists them as legacy products no longer manufactured and proposes the G500 or G100 as replacement. The D.20 I/O modules and the D20E remain usable with the G500.

What they are and where they are used

The GE D20 (in its D20MX, D20/200ME versions and the D.20 modules) are remote terminal units (RTUs) and the GE D400 are substation gateways of the Multilin brand, now GE Vernova. For years they were the link between substations and the control center of many utilities: they collect yard signals and data from relays and meters, and deliver them to the SCADA. The G500 is GE Vernova’s current device for that function, together with the G100.

For the RTU and gateway concept, read the guide on substation RTUs and gateways.

Variants: D20, D400, G500, G100 and iBox

Model	Function	Status according to GE Vernova
D20MX	Substation controller (RTU)	Discontinued; check availability
D20/200ME	Substation controller	Discontinued; alternative G500, or D20MX/D200MX
D.20 RIO	Remote inputs and outputs	Discontinued; alternative G100 or G500
D20E	Input and output module	Works with D20MX and G500
D400	Substation gateway	Discontinued; alternative G100 or G500
iBox	Gateway	Discontinued; alternative G100
G500	Current gateway and controller	Data collection, logging, protocol conversion and automation applications
G100	Current gateway	Alternative GE Vernova indicates for the D400, D.20 RIO and iBox

GE Vernova states that the D.20 input and output modules will remain available for use with G500 products, which allows replacing the processor without rewiring the whole yard.

Main features

Data concentration. The D400 collects measurements, statuses, events and fault records from devices connected by serial port or network.
Secure web HMI. The D400 presents data locally or remotely through a browser (HTTPS).
Inputs and outputs. The D20 RTUs read yard positions and alarms and execute open and close commands through their modules.
Cybersecurity. The D400 supports HTTPS, SSH, TLS, SFTP and SCP, with LDAP, TACACS+ and RADIUS authentication.
Automation. The G500 runs automation applications in addition to protocol conversion.

Communications and integration

For the D400, GE Vernova lists: DNP3 serial and TCP (client and server), IEC 61850 (client), Modbus serial and TCP, IEC 60870-5-101/103/104 (client), IEC 60870-5-101/104 (server), SEL Fast Meter and SEL ASCII, and PRP redundancy per IEC 62439-3. Relay records are retrieved over TFTP, FTP, SFTP, MMS or SEL ASCII. The gateway’s client and server roles, its point database and command testing are covered in Protocol Gateway: DNP3, Modbus and IEC 61850.

In a migration, what cannot change is what the control center sees: the addresses and the point map the SCADA expects. That is why the database of the old device is captured before the new one is configured.

What the D400 offers, according to its brochure

The Multilin D400 brochure (GE Vernova, in English, reference GEA-12806D) describes it as a hardened substation gateway. It collects measurements, statuses, events and fault records from devices over serial or LAN, and summarizes them. It makes them available locally or remotely through a secure browser (HTTPS). The data that matter most when migrating or maintaining one are these:

Ports and media: up to 16 serial ports (RS-232, RS-485 and plastic or glass fiber) and 64 virtual serial ports. It supports up to two Ethernet cards (10/100Base-T, 100Base-FX or 10/100Base-SX) with three independent Ethernet interfaces, each with its own IP and MAC address. It has dual hot-swappable power supplies and an integrated 2- or 4-port Ethernet switch. Hot-swappable communication modules avoid external media converters.
Role by protocol: DNP3 serial and TCP/IP as client and server; IEC 61850 as client; Modbus serial and TCP as client and server; IEC 60870-5-101/103/104 as client and IEC 60870-5-101/104 as server; SEL Fast Meter and SEL ASCII; Hydran and generic ASCII. That is, as an IEC 61850 concentrator it is a client (with dynamic data sets, buffered control blocks and enhanced-security controls); the brochure list does not include an IEC 61850 server role toward the SCADA.
Redundancy: three operating modes (standalone, warm standby and hot standby). In the hybrid model two D400 units synchronize accumulators, event logs and configuration, and the serial links switch according to the health of each unit. The applications listed in hot standby include the DNP3 client and server, the IEC 61850 client, IEC 61131 logic and the firewall. On the network, PRP per IEC 62439-3 edition 2. GE states that D400 units with a CPU of 1 GHz or more can enable PRP through a firmware update. It also states that the device can communicate at the same time over a single LAN, a legacy dual LAN and PRP, which helps in existing installations.
Security: centralized authentication (LDAP, TACACS+ and RADIUS), audit logging over local and remote Syslog, role-based access control, access over SSH, SFTP, SCP, HTTPS and TLS, and TLS tunnels between the master and the D400 for DNP3/TCP, Modbus/TCP and IEC 104. It includes a simple VPN server (OpenVPN) and a whitelist of up to 1,024 rules.
Data logging and reports: analog and digital data logger. It generates analog reports per shift (4, 6, 8 or 12 hours), daily, weekly or monthly in PDF, Excel or HTML. It retrieves records automatically over TFTP, FTP, SFTP, IEC 61850 MMS and GE or SEL ASCII.
Logic: LogicLinx, compliant with IEC 61131, plus an integrated alarm annunciator and single-line diagram editor. It is configured with the SGConfig suite.

The D20E as successor to the D20 I/O

The brochure of the D20E (Ethernet I/O) module presents it as the next generation of input and output modules for the D20. It has the same terminal layout (pin to pin) as the existing D20 I/O, which allows replacing modules without rewiring the yard. There are four types: combined (16 digital inputs, 16 analog inputs and 8 control outputs), status (64 digital inputs), analog (32 inputs) and control (32 outputs). It has 1 ms time stamping, protection-grade output relays rated 8 A DC that, according to the brochure, make auxiliary relays unnecessary, 2,800 Vdc isolation and a range of –40 to +70 °C. It speaks DNP3 and IEC 61850, with two 10/100 Mbps Ethernet ports and one USB port, and is configured with DAPserver Studio. The manufacturer specifies that the D20E must sit behind a server or IED (for example the D20MX or the D400). It must not be connected directly to the substation LAN, because it is not considered an edge device and must be inside the electronic security perimeter. This is a design criterion that conditions the network architecture when replacing a D20.

Frequent mistakes when replacing a D20 or a D400

Losing the master’s behavior. The SCADA expects specific addresses, object types and event behaviors. If the new device changes how DNP3 events are handled, the master may see differences even when the points match.
Forgetting the client role. The D400 is an IEC 61850 client: the list of data sets and reports of each relay must be captured (CID or SCD files) before the old device is switched off.
Changing media without planning the fiber. If the D400 converted to plastic fiber for old relays, the replacement needs that medium or a converter.

Frequent technical questions

D20 or D400 manual: GE Vernova maintains the documentation of legacy devices; the G500 has its own quick start guide and manuals.
D20 spare parts: the D.20 input and output modules remain available; ask the manufacturer about the D20MX processor.
Points that stop reporting: usually a relay that changed its map or address, a serial port with problems or an outdated database.
Time synchronization: time-stamped events depend on the gateway and the relays being synchronized; related topic: time synchronization in substations.

If your device is no longer manufactured

The D20MX, D20/200ME, D400, D.20 RIO and iBox are no longer manufactured. The route GE Vernova proposes is the G500 (or the G100), reusing existing D.20 modules where possible. The migration is planned in stages: capture the database, configure the new device with the same map toward the control center, test point by point and cut over with the least possible outage. We design that migration; see engineering design and studies.

How we can help

Our team configures gateways and RTUs, captures databases of existing devices, integrates relays and meters and runs point-to-point tests with the control center. We load and modify logic, interlocks and signals remotely through remote configuration of Multilin relays and controllers, without waiting for a site visit. Learn more about SCADA and gateway integration and control, protection and communications configuration. For a quote, contact us.

References

GE Vernova, legacy product pages of the Multilin D400 and catalog of legacy gateways and RTUs (D20MX, D20/200ME, D.20 RIO, iBox, D25).
GE Vernova, quick start guide of the G500 gateway.
IEEE 1815 (DNP3); IEC 60870-5-101/104; IEC 62439-3 (PRP and HSR).

Frequently asked questions

What is the GE D400?

It is a GE (now GE Vernova) substation gateway that collects measurements, statuses, events and fault records from substation devices connected by serial port or network, and makes them available to the SCADA or to a secure web browser. GE Vernova states that it is no longer manufactured and recommends the G100 or G500 as an alternative.

What replaces the GE D20 RTU?

GE Vernova lists the D20MX and D20/200ME as discontinued and proposes the G500 as successor; for some cases it mentions the D20MX or D200MX. The D.20 I/O modules remain available for use with the G500, and the D20E module works with the D20MX and with the G500, which allows migrating in stages.

Which protocols does the D400 handle?

According to GE Vernova: DNP3 serial and TCP as client and server, IEC 61850 as client, Modbus serial and TCP, IEC 60870-5-101, 103 and 104 as client, IEC 60870-5-101 and 104 as server and SEL protocols, plus PRP redundancy and record retrieval over FTP, SFTP and MMS.