Download DC System Failure Modes Part 2

Technical Panel Session. Sunday January 11, 2015.
DC System Failure Modes
Part 2
IEEE PES SBC Winter Meeting.
January 11 – 15, 2014. New Orleans, LA
Typical DC Power System
Batteries
Low Volts Disconnect
Discussion:
Types of Battery
Battery
Disconnects
Battery Disconnect
Batteries
Low Voltage
Disconnects
IEEE PES SBC Winter Meeting. January 11 - 15, 2014. New Orleans LA
Typical DC Power System
Battery Disconnect.
A provision for disconnecting an
entire battery plant and/or Individual
battery strings from the system for:
 Maintenance
 Over current protection.
 Battery Cell Replacement.
Two basic types of battery protection.
Not to be confused with a battery
low-voltage disconnect.
 Can be stand alone or integrated.
 Can be a switch with a fuse in-line or a circuit breaker
IEEE PES SBC Winter Meeting. January 11 - 15, 2014. New Orleans LA
Typical DC Power System
Low-Voltage Disconnect
Non-essential load
Essential load
Provides a means to
disconnect the battery
from the load to prevent
over discharge.
LVD in battery line
Either the load or the
batteries can be disconnected.
Essential load
LVD’s in load lines
Non-essential load
Multiple LVD’s in the load line
allow sequenced load shedding –
keep revenue earning loads powered
longer.
IEEE PES SBC Winter Meeting. January 11 - 15, 2014. New Orleans LA
DC System Failure Modes Somewhat
Unique to Telecom?
Curtis Ashton
IEEE PES StaBatt
Winter 2015 (Jan 11) mtg
Sunday Technical Panel Sessions
IEEE PES SBC Winter Meeting. January 11 - 15, 2014. New Orleans LA
Overview
• Things the Telecom Industry Does Differently
Thanks to the FCC
– FCC Best Practices
• No Battery Disconnects in COs
– What this means for Grounding Cable Sizing
• No LVDs in COs
– What This Does to Batteries on OverDischarge
IEEE PES SBC Winter Meeting. January 11 - 15, 2014. New Orleans LA
A Couple of Relevant FCC Best
Practices
• 8-7-0676
– Network Operators Should Not Use Battery
Disconnects at CO Battery Plants
– Network Operators Should Not Use LVDs at CO
Battery Plants
IEEE PES SBC Winter Meeting. January 11 - 15, 2014. New Orleans LA
Battery Disconnects Required by
NEC Outside COs
• Commonly Used Where NEC “Not Covered”
Exemptions for Telecom/Utility Don’t Apply
– e.g. Business Customer Premises, or Collocation Hotels
IEEE PES SBC Winter Meeting. January
11 - 15, 2014. New Orleans LA
Frame Grounding of Trays/ Racks/Stands
w/Brkr Disconnect
• Per NEC 250.122
– Max Ampacities Per 310.15B17 (Single Conductor)
or 610.14A (30-min Multi-Wire)
Typical Disconnect
Brkr Size
Typical
Ah
Typical Short
Ckt Amps
Ground
AWG
Typical
Ampacity
40
100
4,000
10
30
100
300
12,000
8
70
400
1200
18,000
2
173
600
1680
24,000
1/0
259
1000
3000
30,000
2/0
294
1200
4000
40,000
4/0
399
IEEE PES SBC Winter Meeting. January 11 - 15, 2014. New Orleans LA
Typical Breaker I-t Curve
IEEE PES SBC Winter Meeting. January 11 - 15, 2014. New Orleans LA
CO #6 AWG Rack Ground Wire
IEEE PES SBC Winter Meeting. January 11 - 15, 2014. New Orleans LA
Burnt Up on Short Circuit
IEEE PES SBC Winter Meeting. January 11 - 15, 2014. New Orleans LA
LVDs
• LVD Contactors Keep Batteries from Damage Due to
OverDischarge
– Typically Keep Telecom Batteries Above 1.75 V/cell
– At Least One Battery Manufacturer Has LVDs as a Requirement for
Honoring Standard Warranty
• LVLDs vs LVBDs
– False Operations In Telecom Led to More Adoption of LVBDs After
Electronics Changed to Prevent Burnup
– More False Operations (even of LVBDs) Led to FCC Best Practice for
COs
• We’d Rather Sacrifice the Batteries, But Keep Loads Working
– LVBDs Still Sometimes Used Outside the CO Depending on Company
Practice and Priorities
IEEE PES SBC Winter Meeting. January 11 - 15, 2014. New Orleans LA
Damage w/o LVDs
• While Most Telecom Equipment Shuts Itself Off Before Battery
Max Discharge Avg of 1.67 V/Cell, Some will allow Draining
Batteries Below 1.0 V/Cell
IEEE PES SBC Winter Meeting. January 11 - 15, 2014. New Orleans LA
Typical DC Power System
Batteries
Two Main Chemistries:
Lead-Acid
Nickel Cadmium
IEEE PES SBC Winter Meeting. January 11 - 15, 2014. New Orleans LA
Typical DC Power System
Batteries
Two Main Types:
Valve-regulated. (Out gassing is limited by a pressure
relief valve).
Vented. The gasses are allowed to vent from the battery.
They are available in both lead-acid and nickel cadmium
IEEE PES SBC Winter Meeting. January 11 - 15, 2014. New Orleans LA
Typical DC Power System
Batteries
Three main types of Vented Lead-Acid Batteries:
Vented Planté
(Pure Lead)
Plate
Vented Flat (Pasted)
Plate Calcium, Selenium,
and Antimony
Tubular Plate
IEEE PES SBC Winter Meeting. January 11 - 15, 2014. New Orleans LA
Typical DC Power System
Typical VLA (Flooded)
Battery Systems
Note Spill Containment
IEEE PES SBC Winter Meeting. January 11 - 15, 2014. New Orleans LA
Typical DC Power System
Batteries
Two Main Types of Valve-Regulated
Lead-Acid (VRLA) Batteries:
Absorbed (starved) Electrolyte
Gelled Electrolyte
These are mostly Lead-Calcium
but some contain other alloys.
IEEE PES SBC Winter Meeting. January 11 - 15, 2014. New Orleans LA
Typical DC Power System
Typical VRLA 20
Year Batteries.
Large 48 Volt Plant
Small 24 Volt Plant
IEEE PES SBC Winter Meeting. January 11 - 15, 2014. New Orleans LA
Typical DC Power System
Typical 10 Year Front
Terminal Batteries
IEEE PES SBC Winter Meeting. January 11 - 15, 2014. New Orleans LA