Powering Life for Modern Humanity

MTL-Series Unit Substation Switchgear

Unit Substations with Primary Voltage of 2.4kV-38kV, Transformers kVA: 500-20,000 kVA, & Secondary Voltage: 208V-15kV


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APT MTL-Series Secondary Skid-Mounted Unit Substation Switchgear consists of Low & Medium Voltage Switchgear with a power transformer. Moreover, these three units work together to bring service power to the largest facilities. Our MTL-Series certainly offers versatile substations with several configurations.

MTL-Series Unit Substation Switchgear

General Features

  • Built to IEEE Std C37.121-2012: IEEE Guide for Switchgear – Unit Substation – Requirements
  • Frequency: 60Hz or 50Hz
  • Silver plated copper bus
  • Listed low voltage bus ampacity up to 4000A
    • Unlisted options built to UL standards available upon request for main buses larger than 4000A
  • Busbar connections with NEMA standard hole pattern
  • Front or Rear Bus Access for either top or bottom cable entry
  • Low Voltage Power, Insulated Case Circuit Breakers, or Molded Case Circuit Breakers:
  • Installation Location & Enclosure:
    • NEMA 1 for Indoor Installation
    • NEMA 3R for Outdoor Installation
    • Manufactured from Carbon Steel, Aluminum or Stainless Steel (304 or 316)
    • Powder coated ANSI 61 Gray
    • NEMA 1 Lockable T-handles
    • Internal Climate Control (requires 120VAC)
      • Anti-condensation Heater w/Thermostat
    • NEMA 3R Stainless Steel hardware & pad lockable handle
    • Optional Power System Mimic Bus

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MTL-Series Unit Substation Switchgear

Main Components


Medium Voltage Switchgear Features

  • Ratings: 2.4kV – 38kV, 3Ø
  • Main Protection Disconnect Sections Options:
    • IEEE Std C37.20.2 – Metal-clad Drawout Vacuum Circuit Breaker
    • IEEE Std C37.20.3 – Metal-enclosed Fused Air Insulated Loadbreak Interrupter Switch (LIS)
    • Metal-enclosed Unfused Air Insulated Switch with Fixed or Roll Out Vacuum Circuit Breaker
    • Metal-enclosed Drawout Vacuum Circuit Breaker
    • IEEE 386 – Loadbreak or Deadbreak Bushings with Optional Grounding
    • IEEE Std C37.23 – Metal-enclosed Bus Stabs with NEMA Standard 2-hole pattern directly to the transformer or incoming line pull section

Power Transformers

Medium Voltage to Low Voltage


High Voltage Side

  • Aluminum windings
  • 2.4kV – 34,500 V Delta or Wye connected
  • BIL up to 200 kV
  • Tap changer: ± 2, 2.5%
  • Live front
  • Radial feed
  • Optional Bushing wells

Common Features

  • Up to 4MVA Transformers
    • Dry-Type
    • Cast-Coil
    • Oil-Filled
  • Built to all applicable IEEE C57.12.34
  • Cooling Class: ONAN
  • Pad Mount, Step Down
  • Ratings:
    • 500kVA – 4,000 kVA
    • Frequency: 60Hz
    • Impedance: 5.75%
      ± 7.5%
    • Temperature Rise: 149°F
  • Dead Front or Loop Feed Option
  • Enclosure:
    • Indoor NEMA 1 or Outdoor NEMA 3R
    • Mild steel tank & cabinet
    • Powder Paint System; Color: ANSI 70 or Green Munsell 7GY 3.29/1.5
    • Weights: 7000-17500 lbs.

Low Voltage Side

  • Aluminum windings
  • Single Low Voltage Winding
  • 208V – 120 V Delta or Grounded Wye Connected
  • BIL up to 10kV
  • Epoxy 2-piece bushings with 4-holes blade

Low Voltage Switchgear Features

  • Ratings: 208V – 690V, 3Ø
  • ANSI/UL 891 Listed & Labeled Low Voltage Main Protection and Feeder Sections Options:
    • UL 489 Insulated Case & Molded Case Circuit Breakers
    • Built to IEEE Std C37.20.1 with UL 1066 Listed Low Voltage Power Circuit Breakers
  • Interrupting Rating: 18kA – 200kA @ 480VAC
  • Circuit Breaker position Aux Contacts (“a” and “b”)
  • Your Choice of Circuit Breakers:
    • Low Voltage Power Circuit Breakers (LVPCBs)/Insulated Case Circuit Breakers (ICCBs):
      • Available from 100A up to 6000A
      • LVPCBs UL® 1066 Listed
      • ICCBs UL® 489 Listed
      • See page 9 for table of available circuit breaker frame ratings
      • Electrically or Manually Operated
      • 100% Rated
      • Fixed Mounted or Drawout
      • Electronic Trip Units – LI, LSI, LSIG
    • Molded Case Circuit Breakers:
      • UL® 489 Listed
      • Available up to 3000A
      • Manually Operated
      • Electrically Operated with Motor Operator Add-on
      • Standard or 100% Rated
      • Fixed Mounted
      • Thermal Magnetic or Electronic Trip Units – LI, LSI, LSIG

Unit Substation Switchgear

Transfer & Backup Options

  • Automatic Source Transfer for Double Ended Substations:
    • Add secondary paths to provide power to your feeders via a double ended substation
      • As a result, this enables the ability to feed loads from two different utility or generator sources automatically
    • Automatic standby with Open or Closed Transition return operation
    • Call APT for Automatic standby with (Soft loading/Unloading) operation or Sustained Utility Paralleling operation
  • Backup Portable Substations for Integrated Generator/Load Bank Quick Connection
    • Adds the ability to connect temporary power to your unit substation/unit substation switchgear to provide power to your feeders
      • This is done through integrated Generator Quick Connection
      • Backup your ability to feed loads manually via temporary generator connection

Unit Substation Switchgear

Motor Starting, Protection, & Control

  • Add Motor Starting Capability to your Secondary Unit Substation Switchgear
  • Single Phase and Three Phase (115V – 575V) motor controls
  • 0.5HP – 400HP drives in a single standard section
  • Over 400HP through 800HP drives can be housed in larger custom sized sections
  • Hand-Off-Auto control switches and activity indicating lights gives users the ability to control motors from the control panel
  • Terminal blocks as needed for customer field connections
  • Able to house:
    • Variable Frequency Drives
    • Motor SoftStarters
    • Manual Starters
    • Motor Controller Contactors
    • Overload Relays
    • Full Voltage Non-Reversing or Reversing Starters
  • Air Flow cutouts ensure proper cooling for the number of devices

Unit Substation Switchgear & Control Applications

Water & Wastewater Treatment Plants

Data Centers

Healthcare & VA Medical Centers



Electric Utility & Manufacturing


Applicable Standards

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