The "*.ens" format for describing a network is simple. To exemplify it, here's a small network consisting of just two buses and one branch joining them. Lines begining with "#" are omitted when reading the file. Bus and branch records both ocupy only one line, containing the fields described below. It is mandatory that buses appear before branches in the file.

############################################################
# Buses section
#
#   Bus fields are:
#    1: BUS ID: Numeric identifier of the bus
#    2: BUS AREA ID: Numeric identifier of the bus area
#    3: BUS TYPE: Type of the bus (1=SOURCE, 2=NORMAL)
#    4: BUS INJ PWR: Bus injected power, real part, in p.u.
#    5: BUS INJ PWR: Bus injected power, imaginary part, in p.u.
#    6: BUS VOLTAGE: Bus voltage, real part, in p.u.
#    7: BUS VOLTAGE: Bus voltage, imaginary part, in p.u.
#    8: BUS BASE POWER: Bus base power, in KVA
#    9: BUS BASE VOLTAGE: Bus base voltage, in KV
#
############################################################
BUS 1 1 2 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 1.0000e+03 2.5000e+01
BUS 2 1 2 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 1.0000e+03 2.5000e+01


############################################################
# Branches section
#
#   Branch fields are:
#     1: BRANCH ID: Numeric identifier of the branch
#     2: BRANCH TYPE: Type of the branch (0=SWITCH, 1=NORMAL)
#     3: BRANCH VERTEX 1: Identifier of end bus 1
#     4: BRANCH VERTEX 2: Identifier of end bus 2
#     5: BRANCH AREA 1: Area identifier of end bus 1
#     6: BRANCH AREA 2: Area identifier of end bus 2
#     7: BRANCH STATE: Current state of the branch (0=OPEN, 1=CLOSED)
#     8: BRANCH NOMINAL STATE: Nominal state of the branch (0=OPEN, 1=CLOSED)
#     9: BRANCH IMPEDANCE: Impedance of the branch, real part, in p.u.
#    10: BRANCH IMPEDANCE: Impedance of the branch, imaginary part, in p.u.
#    11: BRANCH INTENSITY: Intensity of the branch, real part, in p.u.
#    12: BRANCH INTENSITY: Intensity of the branch, imaginary part, in p.u.
#    13: BRANCH MAX. INTENSITY: Magnitude of the maximum intensity of the branch, in p.u.
#
############################################################
BRANCH 1 0 1 2 1 1 1 1 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 1.0000e+01