inGDB = r"D:mygeodatabase.gdb"
env.workspace = inGDB
#################Getting all Tables and Feature Classes###########
fcs = []
#root of workspace
for item in arcpy.ListFeatureClasses("*"):    fcs.append(item)
for item in arcpy.ListTables("*"):    fcs.append(item)

fds = arcpy.ListDatasets("*","Feature")
for fd in fds:
    env.workspace = inGDB +'\'+fd
    for fc in arcpy.ListFeatureClasses("*"):
        fcs.append(fd+'/'+fc)
    for tb in arcpy.ListTables("*"):
        fcs.append(fd+'/'+tb)

env.workspace = inGDB
relClasses = set()
for i,fc in enumerate(fcs):
    desc = arcpy.Describe(fc)
    for j,rel in enumerate(desc.relationshipClassNames):
        relDesc = arcpy.Describe(rel)
        if relDesc.isAttachmentRelationship:
            continue
        relClasses.add(rel)

print relClasses

arcpy.env.workspace = 'C:/workspace'

# Local variables
tables = arcpy.ListTables()

# Iterate through tables in file geodatabase (workspace)
for t in tables:
    # Get relationship class(es) associated with table
    desc = arcpy.Describe(t)
    rcs = desc.relationshipClassNames
# Iterate through any relationship classes associated with current table in loop
    for r in rcs:
        if len(r) > 30:
            print 'Relationship class ' + r + ' has ' + str(len(r)) + ' characters.'

layer = "C:\Geodatabases\somegeodatabase.gdb\my_layer"
desc = arcpy.Describe(layer)
print desc.relationshipClassNames